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A119733 Offsets of the terms of the nodes of the reverse Collatz function. 2
0, 1, 2, 5, 4, 7, 10, 19, 8, 11, 14, 23, 20, 29, 38, 65, 16, 19, 22, 31, 28, 37, 46, 73, 40, 49, 58, 85, 76, 103, 130, 211, 32, 35, 38, 47, 44, 53, 62, 89, 56, 65, 74, 101, 92, 119, 146, 227, 80, 89, 98, 125, 116, 143, 170, 251, 152, 179, 206, 287, 260, 341, 422, 665, 64, 67 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,3

COMMENTS

Create a binary tree starting with x. To follow 0 from the root, apply f(x)=2x. To follow 1, apply g(x)=(2x-1)/3. For example, starting with x, the string 010 {also known as f(g(f(x))) }, you would get (8x-2)/3. These expressions represent the reverse Collatz function and will provide numbers whose Collatz path may include x. These expressions will all be of the form (2^a*x-b)/3^c. This sequence concerns b. What makes b interesting is that if you draw the tree, each level of the tree will have the same sequence of values for b. The root of the tree x, can be written as (2^0*x-0)/3^0, which has the first value for b. Each subsequent level contains twice as many values of b.

This sequence is 0 followed by a permutation of A213539, and therefore consists of 0 plus the elements of A116640 multiplied by 2^k, where k >= 0. E.g., 1, 5, 7, 19 becomes 0, 2^0*1, 2^1*1, 2^0*5, 2^2*1, 2^0*7, 2^1*5, 2^0*19 ... - Joe Slater, Dec 19 2016

When this sequence is arranged as an irregular triangle the sum of each row a(2^k)...a(2^(k+1)-1) equals A081039(2^k). The cumulative sum from a(0) to a(2^k-1) equals A002697(k). - Joe Slater, Apr 12 2018

LINKS

Alois P. Heinz, Table of n, a(n) for n = 0..16383

FORMULA

a(0) = 0, a(2n + 1) = 2a(n) + 3^wt(n) = 2a(n) + A048883(n), a(2n) = 2a(n), where wt(n) = A000120(n) = the number 1's in the binary representation of n.

a(k) = [z^k] 1 + (1/(1-z)) * Sum_{s=0..n-1} 2^s*z^(2^s)*(1 - z^(2^s)) * Product_{r=s+1..n-1} (1 + 3*z^(2^r)), for 0 < k <= 2^n-1. - Wolfgang Hintze, Jul 28 2017

EXAMPLE

a(1) = 1 = 2 * 0 + 3^0 since 0 written in binary contains no 1's.

MAPLE

a:= proc(n) `if`(n=0, 0, `if`(irem(n, 2, 'r')=0, 0,

      3^add(i, i=convert(r, base, 2)))+2*a(r))

    end:

seq(a(n), n=0..127);  # Alois P. Heinz, Aug 13 2017

MATHEMATICA

a[0] := 0; a[n_?OddQ] := 2a[(n - 1)/2] + 3^Plus@@IntegerDigits[(n - 1)/2, 2]; a[n_?EvenQ] := 2a[n/2]; Table[a[n], {n, 0, 65}] (* Alonso del Arte, Apr 21 2011 *)

PROG

(Perl) # call with n to get 2^n values

$depth=shift; sub funct { my ($i, $b, $c) = @_; if ($i < $depth) { funct($i+1, $b*2, $c); funct($i+1, 2*$b+$c, $c*3); } else { print "$b, "; } } funct(0, 0, 1); print " ";

(Python)

from sympy.core.cache import cacheit

@cacheit

def a(n): return 0 if n==0 else 2*a((n - 1)/2) + 3**bin((n - 1)/2).count('1') if n%2==1 else 2*a(n/2)

print map(a, xrange(131)) # Indranil Ghosh, Aug 13 2017

CROSSREFS

Cf. A002697, A081039, A116623, A116640, A116641, A213539, A226383.

Sequence in context: A296203 A036237 A015948 * A140869 A111570 A057954

Adjacent sequences:  A119730 A119731 A119732 * A119734 A119735 A119736

KEYWORD

nonn

AUTHOR

William Entriken, Jun 14 2006

STATUS

approved

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Last modified December 17 06:45 EST 2018. Contains 318192 sequences. (Running on oeis4.)