

A001950


Upper Wythoff sequence (a Beatty sequence): a(n) = floor(n*phi^2), where phi = (1+sqrt(5))/2.
(Formerly M1332 N0509)


253



2, 5, 7, 10, 13, 15, 18, 20, 23, 26, 28, 31, 34, 36, 39, 41, 44, 47, 49, 52, 54, 57, 60, 62, 65, 68, 70, 73, 75, 78, 81, 83, 86, 89, 91, 94, 96, 99, 102, 104, 107, 109, 112, 115, 117, 120, 123, 125, 128, 130, 133, 136, 138, 141, 143, 146, 149, 151, 154, 157
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OFFSET

1,1


COMMENTS

Indices at which blocks (1;0) occur in infinite Fibonacci word; i.e., n such that A005614(n2) = 0 and A005614(n1) = 1.  Benoit Cloitre, Nov 15 2003
A000201 and this sequence may be defined as follows: Consider the maps a > ab, b > a, starting from a(1) = a; then A000201 gives the indices of a, A001950 gives the indices of b. The sequence of letters in the infinite word begins a, b, a, a, b, a, b, a, a, b, a, ... Setting a = 0, b = 1 gives A003849 (offset 0); setting a = 1, b = 0 gives A005614 (offset 0).  Philippe Deléham, Feb 20 2004
a(n) = nth integer which is not equal to the floor of any multiple of phi, where phi = (1+sqrt(5))/2 = golden number.  Philippe LALLOUET (philip.lallouet(AT)wanadoo.fr), May 09 2007
Write A for A000201 and B for the present sequence (the upper Wythoff sequence, complement of A). Then the composite sequences AA, AB, BA, BB, AAA, AAB, ..., BBB, ... appear in many complementary equations having solution A000201 (or equivalently, the present sequence). Typical complementary equations: AB=A+B (=A003623), BB=A+2B (=A101864), BBB=3A+5B (=A134864).  Clark Kimberling, Nov 14 2007
Apart from the initial 0 in A090909, is this the same as that sequence?  Alec Mihailovs (alec(AT)mihailovs.com), Jul 23 2007
If we define a basephi integer as a positive number whose representation in the golden ratio base consists only of nonnegative powers of phi, and if these basephi integers are ordered in increasing order (beginning 1, phi, ...), then it appears that the difference between the nth and (n1)th basephi integer is phi1 if and only if n belongs to this sequence, and the difference is 1 otherwise. Further, if each basephi integer is written in linear form as a + b*phi (for example, phi^2 is written as 1 + phi), then it appears that there are exactly two basephi integers with b=n if and only if n belongs to this sequence, and exactly three basephi integers with b=n otherwise.  Geoffrey Caveney, Apr 17 2014
Numbers with an odd number of trailing zeros in their Zeckendorf representation (A014417).  Amiram Eldar, Feb 26 2021


REFERENCES

Claude Berge, Graphs and Hypergraphs, NorthHolland, 1973; p. 324, Problem 2.
Eric Friedman, Scott M. Garrabrant, Ilona K. PhippsMorgan, A. S. Landsberg and Urban Larsson, Geometric analysis of a generalized Wythoff game, in Games of no Chance 5, MSRI publ. Cambridge University Press, 2019.
Martin Gardner, Penrose Tiles to Trapdoor Ciphers, W. H. Freeman, 1989; see p. 107.
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).
I. M. Yaglom, Two games with matchsticks, pp. 17 of Qvant Selecta: Combinatorics I, Amer Math. Soc., 2001.


LINKS

Eric Duchene, Aviezri S. Fraenkel, Vladimir Gurvich, Nhan Bao Ho, Clark Kimberling, and Urban Larsson, Wythoff Wisdom, 43 pages, no date, unpublished.
Eric Duchene, Aviezri S. Fraenkel, Vladimir Gurvich, Nhan Bao Ho, Clark Kimberling, and Urban Larsson, Wythoff Wisdom, unpublished, no date [Cached copy, with permission]
Aviezri S. Fraenkel, The Raleigh game, INTEGERS: Electronic Journal of Combinatorial Number Theory 7.2 (2007): A13, 10 pages. See Table 1.
Aviezri S. Fraenkel, Ratwyt, December 28 2011.
D. J. Newman, Problem 5252, Amer. Math. Monthly, Vol. 72, No. 10 (1965), pp. 11441145.


FORMULA

a(n) = n + floor(n*phi). In general, floor(n*phi^m) = Fibonacci(m1)*n + floor(Fibonacci(m)*n*phi).  Benoit Cloitre, Mar 18 2003
Append a 0 to the Zeckendorf expansion (cf. A035517) of nth term of A000201.
If a'=A000201 is the ordered complement (in N) of {a(n)}, then a(Fib(r2) + j) = Fib(r) + a(j) for 0 < j <= Fib(r2), 3 < r; and a'(Fib(r1) + j) = Fib(r) + a'(j) for 0 < j <= Fib(r2), 2 < r.  Paul Weisenhorn, Aug 18 2012
With a(1)=2, a(2)=5, a'(1)=1, a'(2)=3 and 1 < k and a(k1) < n <= a(k) one gets a(n)=3*nk, a'(n)=2*nk.  Paul Weisenhorn, Aug 21 2012


EXAMPLE

a(14) = floor(14*phi^2) = 36; a'(14) = floor(14*phi)=22;
with r=9 and j=1: a(13+1) = 34 + 2 = 36;
with r=8 and j=1: a'(13+1) = 21 + 1 = 22.
k=6 and a(5)=13 < n <= a(6)=15
a(14) = 3*14  6 = 36; a'(14) = 2*14  6 = 22;
a(15) = 3*15  6 = 39; a'(15) = 2*15  6 = 24. (End)


MAPLE

floor(n*(3+sqrt(5))/2) ;
end proc:


MATHEMATICA

Table[Floor[N[n*(1+Sqrt[5])^2/4]], {n, 1, 75}]


PROG

(PARI) a(n)=floor(n*(sqrt(5)+3)/2)
(Haskell)
(Magma) [Floor(n*((1+Sqrt(5))/2)^2): n in [1..80]]; // Vincenzo Librandi, Nov 19 2016
(Python)
from math import isqrt


CROSSREFS

a(n) = greatest k such that s(k) = n, where s = A026242.
First differences give (essentially) A076662.
The following sequences are all essentially the same, in the sense that they are simple transformations of each other, with A000201 as the parent: A000201, A001030, A001468, A001950, A003622, A003842, A003849, A004641, A005614, A014675, A022342, A088462, A096270, A114986, A124841.  N. J. A. Sloane, Mar 11 2021


KEYWORD

nonn,easy,nice


AUTHOR



EXTENSIONS



STATUS

approved



