

A001511


The ruler function: 2^a(n) divides 2n. Or, a(n) = 2adic valuation of 2n.
(Formerly M0127 N0051)


408



1, 2, 1, 3, 1, 2, 1, 4, 1, 2, 1, 3, 1, 2, 1, 5, 1, 2, 1, 3, 1, 2, 1, 4, 1, 2, 1, 3, 1, 2, 1, 6, 1, 2, 1, 3, 1, 2, 1, 4, 1, 2, 1, 3, 1, 2, 1, 5, 1, 2, 1, 3, 1, 2, 1, 4, 1, 2, 1, 3, 1, 2, 1, 7, 1, 2, 1, 3, 1, 2, 1, 4, 1, 2, 1, 3, 1, 2, 1, 5, 1, 2, 1, 3, 1, 2, 1, 4, 1, 2, 1, 3, 1, 2, 1, 6, 1, 2, 1, 3, 1, 2, 1, 4, 1
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OFFSET

1,2


COMMENTS

a(n)  1 is the number of trailing zeros in the binary expansion of n.
If you are counting in binary and the least significant bit is numbered 1, the next bit is 2, etc., a(n) is the bit that is incremented when increasing from n1 to n.  Jud McCranie, Apr 26 2004
Number of steps to reach an integer starting with (n+1)/2 and using the map x > x*ceiling(x) (cf. A073524).
a(n) is the number of the disk to be moved at the nth step of the optimal solution to Towers of Hanoi problem (comment from Andreas M. Hinz).
Shows which bit to flip when creating the binary reflected Gray code (bits are numbered from the right, offset is 1). This is essentially equivalent to Hinz's comment.  Adam Kertesz, Jul 28 2001
a(n) is the Hamming distance between n and n1 (in binary). This is equivalent to Kertesz's comments above.  TakShing Chan (chan12(AT)alumni.usc.edu), Feb 25 2003
Let S(0) = {1}, S(n) = {S(n1), S(n1){x}, x+1} where x = last term of S(n1); sequence gives S(infinity).  Benoit Cloitre, Jun 14 2003
The sum of all terms up to and including the first occurrence of m is 2^m1.  Donald Sampson (marsquo(AT)hotmail.com), Dec 01 2003
m appears every 2^m terms starting with the 2^(m1)th term.  Donald Sampson (marsquo(AT)hotmail.com), Dec 08 2003
Relation to C(n) = Collatz function iteration using only odd steps: a(n) is the number of right bits set in binary representation of A004767(n) (numbers of the form 4*m+3). So for m=A004767(n) it follows that there are exactly a(n) recursive steps where m<C(m).  Lambert Klasen (lambert.klasen(AT)gmx.de), Jan 23 2005
Between every two instances of any positive integer m there are exactly m distinct values (1 through m1 and one value greater than m).  Franklin T. AdamsWatters, Sep 18 2006
Every prefix up to (but not including) the first occurrence of some k >= 2 is a palindrome.  Gary W. Adamson, Sep 24 2008
1 interleaved with (2 interleaved with (3 interleaved with ( ... ))).  Eric D. Burgess (ericdb(AT)gmail.com), Oct 17 2009
Given A000041, P(x) = A(x)/A(x^2) with P(x) = (1 + x + 2x^2 + 3x^3 + 5x^4 + 7x^5 + ...), A(x) = (1 + x + 3x^2 + 4x^3 + 10x^4 + 13x^5 + ...), A(x^2) = (1 + x^2 + 3x^4 + 4x^6 + 10x^8 + ...), where A092119 = (1, 1, 3, 4, 10, ...) = Euler transform of the ruler sequence, A001511.  Gary W. Adamson, Feb 11 2010
Subtracting 1 from every term and deleting any 0's yields the same sequence, A001511.  Ben Branman, Dec 28 2011
In the listing of the compositions of n as lists in lexicographic order, a(k) is the last part of composition(k) for all k <= 2^(n1) and all n, see example.  Joerg Arndt, Nov 12 2012
According to Hinz, et al. (see links), this sequence was studied by Louis Gros in his 1872 pamphlet "Théorie du Baguenodier" and has therefore been called the Gros sequence.
First n terms comprise least squarefree word of length n using positive integers, where "squarefree" means that the word contains no consecutive identical subwords; e.g., 1 contains no square; 11 contains a square but 12 does not; 121 contains no square; both 1211 and 1212 have squares but 1213 does not; etc.  Clark Kimberling, Sep 05 2013
Length of 0run starting from 2 (10, 100, 110, 1000, 1010, ...), or length of 1run starting from 1 (1, 11, 101, 111, 1001, 1011, ...) of every second number, from right to left in binary representation.  Armands Strazds, Apr 13 2017
a(n) is also the frequency of the largest part in the integer partition having viabin number n. The viabin number of an integer partition is defined in the following way. Consider the southeast border of the Ferrers board of the integer partition and consider the binary number obtained by replacing each east step with 1 and each north step, except the last one, with 0. The corresponding decimal form is, by definition, the viabin number of the given integer partition. "Viabin" is coined from "via binary". For example, consider the integer partition [2,2,2,1]. The southeast border of its Ferrers board yields 10100, leading to the viabin number 20.  Emeric Deutsch, Jul 24 2017
As A000005(n) equals the number of even divisors of 2n and A001227(n) = A001227(2n), the formula A001511(n) = A000005(n)/A001227(n) might be read as "The number of even divisors of 2n is always divisible by the number of odd divisors of 2n" (where number of divisors means sum of zeroth powers of divisors). Conjecture: For any nonnegative integer k, the sum of the kth powers of even divisors of n is always divisible by the sum of the kth powers of odd divisors of n.  Ivan N. Ianakiev, Jul 06 2019
To construct the sequence, start from 1's separated by a place 1,,1,,1,,1,,1,,1,,1,,1,,1,,1,,1,,1,,1,,1,...
Then put the 2's in every other remaining place
1,2,1,,1,2,1,,1,2,1,,1,2,1,,1,2,1,,1,2,1,,1,2,1,...
Then the 3's in every other remaining place
1,2,1,3,1,2,1,,1,2,1,3,1,2,1,,1,2,1,3,1,2,1,,1,2,1,...
Then the 4's in every other remaining place
1,2,1,3,1,2,1,4,1,2,1,3,1,2,1,,1,2,1,3,1,2,1,4,1,2,1,...
By iterating this process, we get the ruler function 1,2,1,3,1,2,1,4,1,2,1,3,1,2,1,5,1,2,1,3,1,2,1,4,1,2,1,... (End)
a(n) is the smallest positive integer that does not occur in the coincidences of the sequence so far a(1..n1) and its reverse.  Neal Gersh Tolunsky, Jan 18 2023


REFERENCES

J.P. Allouche and J. Shallit, Automatic Sequences, Cambridge Univ. Press, 2003.
E. R. Berlekamp, J. H. Conway and R. K. Guy, Winning Ways, Academic Press, NY, 2 vols., 2nd ed., 20012003; see Dim and Dim+ on p. 98; Dividing Rulers, on pp. 436437; The Ruler Game, pp. 469470; Ruler Fours, Fives, ... Fifteens on p. 470.
L. Gros, Théorie du Baguenodier, Aimé Vingtrinier, Lyon, 1872.
A. M. Hinz, The Tower of Hanoi, in Algebras and combinatorics (Hong Kong, 1997), 277289, Springer, Singapore, 1999.
D. E. Knuth, The Art of Computer Programming, vol. 4A, Combinatorial Algorithms, Section 7.1.3, Problem 41, p. 589.
Andrew Schloss, "Towers of Hanoi" composition, in The Digital Domain. Elektra/Asylum Records 9 603032, 1983. Works by Jaffe (Finale to "Silicon Valley Breakdown"), McNabb ("Love in the Asylum"), Schloss ("Towers of Hanoi"), Mattox ("Shaman"), Rush, Moorer ("Lions are Growing") and others.
N. J. A. Sloane, A Handbook of Integer Sequences, Academic Press, 1973 (includes this sequence).
N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).


LINKS

J. C. Lagarias and N. J. A. Sloane, Approximate squaring (pdf, ps), Experimental Math., 13 (2004), 113128.
Joseph Rosenbaum, Elementary Problem E319, American Mathematical Monthly, volume 45, number 10, December 1938, pages 694696. (The A indices in P at equations 1 and 2.)


FORMULA

Multiplicative with a(p^e) = e+1 if p = 2; 1 if p > 2.  David W. Wilson, Aug 01 2001
For any real x > 1/2: lim_{N>infinity} (1/N)*Sum_{n=1..N} x^(a(n)) = 1/(2*x1); also lim_{N>infinity} (1/N)*Sum_{n=1..N} 1/a(n) = log(2).  Benoit Cloitre, Nov 16 2001
s(n) = Sum_{k=1..n} a(k) is asymptotic to 2*n since s(n) = 2*n  A000120(n).  Benoit Cloitre, Aug 31 2002
For any n >= 0, for any m >= 1, a(2^m*n + 2^(m1)) = m.  Benoit Cloitre, Nov 24 2002
a(n) = Sum_{d divides n and d is odd} mu(d)*tau(n/d).  Vladeta Jovovic, Dec 04 2002
G.f.: A(x) = Sum_{k>=0} x^(2^k)/(1x^(2^k)).  Ralf Stephan, Dec 24 2002
a(1) = 1; for n > 1, a(n) = a(n1) + (1)^n*a(floor(n/2)).  Vladeta Jovovic, Apr 25 2003
A fixed point of the mapping 1>12; 2>13; 3>14; 4>15; 5>16; ... .  Philippe Deléham, Dec 13 2003
Ordinal transform of A003602.  Franklin T. AdamsWatters, Aug 28 2006 (The ordinal transform of a sequence b_0, b_1, b_2, ... is the sequence a_0, a_1, a_2, ... where a_n is the number of times b_n has occurred in {b_0 ... b_n}.)
Could be extended to n <= 0 using a(n) = a(n), a(0) = 0, a(2*n) = a(n)+1 unless n=0.  Michael Somos, Sep 30 2006
Sequence = A129360 * A000005 = M*V, where M = an infinite lower triangular matrix and V = d(n) as a vector: [1, 2, 2, 3, 2, 4, ...].  Gary W. Adamson, Apr 15 2007
Dirichlet g.f.: zeta(s)*2^s/(2^s1).  Ralf Stephan, Jun 17 2007
a(n) = Sum_{d divides n} mu(2*d)*tau(n/d).  Benoit Cloitre, Jun 21 2007
G.f.: x/(1x) = Sum_{n>=1} a(n)*x^n*( 1  x^n ).  Paul D. Hanna, Jun 22 2007
With S(n): 2^n  1 first elements of the sequence then S(0) = {} (empty list) and if n > 0, S(n) = S(n1), n, S(n1).  Yann David (yann_david(AT)hotmail.com), Mar 21 2010
a(n+1) = 1 + Sum_{j=0..ceiling(log_2(n+1))} (j * (1  abs(sign((n mod 2^(j + 1))  2^j + 1)))).  Enrico Borba, Oct 01 2015
a(n) = log_2((Xor(2*n,2*n1)+1)/2).  Gary Detlefs, Dec 13 2018
(2^(a(n)1)1)*(n mod 4) = 2*floor(((n+1) mod 4)/3).  Gary Detlefs, Dec 14 2018
a(n) = Sum_{j=1..r} (j/2^j)*(Product_{k=1..j} (1  (1)^floor( (n+2^(j1))/2^(k1) )), for n < a predefined 2^r.  Adriano Caroli, Sep 30 2019


EXAMPLE

For example, 2^12, 2^24, 2^16, 2^38, 2^110, 2^212, ... giving the initial terms 1, 2, 1, 3, 1, 2, ...
Triangle begins:
1;
2,1;
3,1,2,1;
4,1,2,1,3,1,2,1;
5,1,2,1,3,1,2,1,4,1,2,1,3,1,2,1;
6,1,2,1,3,1,2,1,4,1,2,1,3,1,2,1,5,1,2,1,3,1,2,1,4,1,2,1,3,1,2,1;
7,1,2,1,3,1,2,1,4,1,2,1,3,1,2,1,5,1,2,1,3,1,2,1,4,1,2,1,3,1,2,1,6,1,2,1,3,...
(End)
S(0) = {} S(1) = 1 S(2) = 1, 2, 1 S(3) = 1, 2, 1, 3, 1, 2, 1 S(4) = 1, 2, 1, 3, 1, 2, 1, 4, 1, 2, 1, 3, 1, 2, 1.  Yann David (yann_david(AT)hotmail.com), Mar 21 2010
The 16 compositions of 5 as lists in lexicographic order:
[ n] a(n) composition
[ 1] [ 1] [ 1 1 1 1 1 ]
[ 2] [ 2] [ 1 1 1 2 ]
[ 3] [ 1] [ 1 1 2 1 ]
[ 4] [ 3] [ 1 1 3 ]
[ 5] [ 1] [ 1 2 1 1 ]
[ 6] [ 2] [ 1 2 2 ]
[ 7] [ 1] [ 1 3 1 ]
[ 8] [ 4] [ 1 4 ]
[ 9] [ 1] [ 2 1 1 1 ]
[10] [ 2] [ 2 1 2 ]
[11] [ 1] [ 2 2 1 ]
[12] [ 3] [ 2 3 ]
[13] [ 1] [ 3 1 1 ]
[14] [ 2] [ 3 2 ]
[15] [ 1] [ 4 1 ]
[16] [ 5] [ 5 ]
a(n) is the last part in each list.
(End)
Also written as a triangle in which the right border gives A000027 and row lengths give A011782 and row sums give A000079 the sequence begins:
1;
2;
1,3;
1,2,1,4;
1,2,1,3,1,2,1,5;
1,2,1,3,1,2,1,4,1,2,1,3,1,2,1,6;
1,2,1,3,1,2,1,4,1,2,1,3,1,2,1,5,1,2,1,3,1,2,1,4,1,2,1,3,1,2,1,7;
(End)
G.f. = x + 2*x^2 + x^3 + 3*x^4 + x^5 + 2*x^6 + x^7 + 4*x^8 + x^9 + 2*x^10 + ...


MAPLE

# This is the binary logarithm of the denominator of (256^n1)B_{8n}/n, in Maple parlance a := n > log[2](denom((256^n1)*bernoulli(8*n)/n)).  Peter Luschny, May 31 2009
a:= n> ilog2((Bits[Xor](2*n, 2*n1)+1)/2): seq(a(n), n=1..50); # Gary Detlefs, Dec 13 2018


MATHEMATICA

Array[ If[ Mod[ #, 2] == 0, FactorInteger[ # ][[1, 2]], 0] &, 105] + 1 (* or *)
Nest[ Flatten[ # /. a_Integer > {1, a + 1}] &, {1}, 7] (* Robert G. Wilson v, Mar 04 2005 *)
myHammingDistance[n_, m_] := Module[{g = Max[m, n], h = Min[m, n]}, b1 = IntegerDigits[g, 2]; b2 = IntegerDigits[h, 2, Length[b1]]; HammingDistance[b1, b2]] (* Vladimir Shevelev A206853 *) Table[ myHammingDistance[n, n  1], {n, 111}] (* Robert G. Wilson v, Apr 05 2012 *)
Table[Position[Reverse[IntegerDigits[n, 2]], 1, 1, 1], {n, 110}]//Flatten (* Harvey P. Dale, Aug 18 2017 *)


PROG

(PARI) a(n) = sum(k=0, floor(log(n)/log(2)), floor(n/2^k)floor((n1)/2^k)) /* Ralf Stephan */
(PARI) a(n)=if(n%2, 1, factor(n)[1, 2]+1) /* Jon Perry, Jun 06 2004 */
(PARI) {a(n) = if( n, valuation(n, 2) + 1, 0)}; /* Michael Somos, Sep 30 2006 */
(PARI) {a(n)=if(n==1, 1, polcoeff(xsum(k=1, n1, a(k)*x^k*(1x^k)*(1x+x*O(x^n))), n))} /* Paul D. Hanna, Jun 22 2007 */
(Haskell)
a001511 n = length $ takeWhile ((== 0) . (mod n)) a000079_list
(Haskell) a001511 n  odd n = 1  otherwise = 1 + a001511 (n `div` 2)
(Sage) [valuation(2*n, 2) for n in (1..105)] # Bruno Berselli, Nov 23 2015
(Magma) [Valuation(2*n, 2): n in [1..105]]; // Bruno Berselli, Nov 23 2015
(MATLAB) nmax=5; r=1; for n=2:nmax; r=[r n r]; end % Adriano Caroli, Feb 26 2016
(Python)
def a(n): return bin(n)[2:][::1].index("1") + 1 # Indranil Ghosh, May 11 2017
(Python)
(Scheme) (define (A001511 n) (let loop ((n n) (e 1)) (if (odd? n) e (loop (/ n 2) (+ 1 e))))) ;; Antti Karttunen, Oct 06 2017


CROSSREFS

This is Guy Steele's sequence GS(4, 2) (see A135416).
Cf. A000005, A000041, A000079, A003188, A003278, A003602, A007949, A018238, A047999, A051731, A054525, A054852, A065176, A089080, A092119, A117303, A129360, A130093, A173238, A181988, A220466.


KEYWORD

mult,nonn,nice,easy,core,hear


AUTHOR



STATUS

approved



