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A327638 a(0)=1, a(1)=5; for n > 2, a(n) is the smallest odd number j not divisible by 3 such that (3*j+1)/2^k = a(n-1) for some k. 1
1, 5, 13, 17, 11, 7, 37, 49, 65, 43, 229, 305, 203, 541, 721, 961, 5125, 6833, 4555, 6073, 32389, 172741, 230321, 153547, 818917, 4367557, 5823409, 7764545, 5176363, 6901817, 18404845, 98159173, 523515589, 2792083141, 3722777521, 19854813445, 105892338373 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,2

COMMENTS

Also a reverse Collatz sequence with odd numbers. - Paul Conradi, Oct 23 2020

Odd numbers in A225570. - Michel Marcus, Oct 24 2020

LINKS

Michel Marcus, Table of n, a(n) for n = 0..295

FORMULA

If a(n-1) == 1 (mod 3) then a(n) = (4*a(n-1)-1)/3 or (16*a(n-1)-1)/3, whichever value is not divisible by 3.

If a(n-1) == -1 (mod 3) then a(n) = (2*a(n-1)-1)/3 or a(n)=(8*a(n-1)-1)/3, whichever value is not divisible by 3.

EXAMPLE

a(0)=1, a(1)=5 by definition, then a(2) = (2*5-1)/3 or (8*5-1)/3; as (2*5-1)/3 is divisible by 3, a(2) = (8*5-1)/3 = 13.

PROG

(PARI) lista(nn) = {print1(1, ", ", 5); x = 5; for (n = 2, nn, if(x%3 == 1, x = (4*x-1)/3, x = (2*x-1)/3); if(x%3 == 0, x = 4*x + 1); print1(", ",  x)); } \\ Jinyuan Wang, Sep 21 2019

CROSSREFS

Intersection of A005408 and A225570.

Sequence in context: A158334 A282747 A088908 * A092218 A049092 A103666

Adjacent sequences:  A327635 A327636 A327637 * A327639 A327640 A327641

KEYWORD

nonn

AUTHOR

Pierre CAMI, Sep 20 2019

EXTENSIONS

More terms from Jinyuan Wang, Sep 21 2019

STATUS

approved

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Last modified April 11 10:07 EDT 2021. Contains 342886 sequences. (Running on oeis4.)