A325425 a(n) is the least number not 2*a(m) or floor(3*a(m)/2) for any m < n.

1, 3, 5, 8, 9, 11, 14, 15, 17, 19, 20, 23, 24, 26, 27, 29, 31, 32, 33, 35, 37, 41, 42, 44, 45, 47, 50, 51, 53, 56, 57, 59, 60, 65, 68, 69, 71, 72, 73, 77, 78, 80, 81, 83, 86, 87, 89, 91, 92, 93, 95, 96, 98, 99, 101, 104, 105, 107, 110, 111, 113, 116, 119

Offset: 1

Author

Clark Kimberling, Apr 27 2019

Keywords

• nonn
• easy

Comments

The sequence necessarily starts with 1. The next 2 terms are determined as follows: because a(1) = 1, the number 2 is disallowed, so that a(2) = 3, whence the numbers 4 and 6 are disallowed, and a(3) = 5. See A325417 for a guide to related sequences.

Links

• Clark Kimberling, Table of n, a(n) for n = 1..10000

Crossrefs

Cf. A325417, A325426.

Programs

Mathematica

a = {1}; Do[AppendTo[a, NestWhile[# + 1 &, Last[a] + 1, Apply[Or,
Map[MemberQ[a, #] &, Select[Flatten[{#/2,
If[Mod[#, 3] == 0, (2 #)/3, 0] + If[Mod[#, 3] == 1, 1/3 (1 + 2 #), 0]}],
IntegerQ || # == 0]]] &]], {150}]; a (* A325425 *)
Complement[Range[Last[a]], a];       (* A325426 *)
(* Peter J. C. Moses, Apr 25 2019 *)