A037108 Trajectory of 3 under map n->21*n+1 if n odd, n->n/2 if n even.

3, 64, 32, 16, 8, 4, 2, 1, 22, 11, 232, 116, 58, 29, 610, 305, 6406, 3203, 67264, 33632, 16816, 8408, 4204, 2102, 1051, 22072, 11036, 5518, 2759, 57940, 28970, 14485, 304186, 152093, 3193954, 1596977, 33536518, 16768259, 352133440, 176066720, 88033360, 44016680, 22008340

Offset

0,1

Links

Table of n, a(n) for n=0..42.

Formula

a(n) = A033967(n-7), n>=7. - R. J. Mathar, Nov 21 2014

Example

a(2) = 64 as a(1) = 3 and 3 is odd so a(2) = 21*a(1) + 1 = 21*3 + 1 = 64. - David A. Corneth, Jun 24 2025

Maple

a:= proc(n) option remember; `if`(n=0, 3,
      (t-> `if`(t::odd, 21*t+1, t/2))(a(n-1)))
    end:
seq(a(n), n=0..42);  # Alois P. Heinz, Jun 24 2025

Mathematica

NestList[If[OddQ[#], 21*# + 1, #/2] &, 3, 50] (* Paolo Xausa, Jun 25 2025 *)

Crossrefs

Cf. A033967.

Sequence in context: A193100 A053857 A175985 * A249097 A092901 A099338

Adjacent sequences: A037105 A037106 A037107 * A037109 A037110 A037111

Keyword

nonn,easy

Author

N. J. A. Sloane

Status

approved