A274155 Number of integers in n-th generation of tree T(-5/2) defined in Comments.

1, 1, 1, 2, 2, 4, 6, 8, 12, 19, 28, 42, 63, 95, 145, 212, 321, 479, 723, 1080, 1622, 2436, 3652, 5472, 8212, 12309, 18488, 27718, 41599, 62370, 93578, 140360, 210511, 315787, 473646, 710583, 1065773, 1598933, 2398260, 3597426, 5395845, 8093416, 12140388, 18210490, 27317995

Offset: 0

Author

Clark Kimberling, Jun 12 2016

Keywords

• nonn
• easy

Comments

Let T* be the infinite tree with root 0 generated by these rules: if p is in T*, then p+1 is in T* and x*p is in T*. Let g(n) be the set of nodes in the n-th generation, so that g(0) = {0}, g(1) = {1}, g(2) = {2,x}, g(3) = {3,2x,x+1,x^2}, etc. Let T(r) be the tree obtained by substituting r for x.

See A274142 for a guide to related sequences.

Examples

			For r = -5/2, we have g(3) = {3,2r,r+1, r^2}, in which the number of integers is a(3) = 2.
		

Links

• Kenny Lau, Table of n, a(n) for n = 0..48

Crossrefs

Cf. A274142.

Programs

Mathematica

z = 18; t = Join[{{0}}, Expand[NestList[DeleteDuplicates[Flatten[Map[{# + 1, x*#} &, #], 1]] &, {1}, z]]];
u = Table[t[[k]] /. x -> -5/2, {k, 1, z}]; Table[
Count[Map[IntegerQ, u[[k]]], True], {k, 1, z}](*A274155*)

Extensions

More terms from Kenny Lau, Jun 30 2017