A325429 a(n) is the least number not 3*a(m) or floor(3*a(m)/2) for any m < n.

1, 2, 4, 5, 8, 9, 10, 11, 14, 17, 18, 19, 20, 22, 23, 26, 29, 31, 32, 35, 36, 37, 38, 40, 41, 44, 45, 47, 49, 50, 53, 56, 58, 59, 62, 63, 64, 65, 68, 71, 72, 74, 76, 77, 80, 81, 82, 83, 85, 86, 89, 90, 91, 92, 95, 98, 99, 100, 101, 103, 104, 107, 109, 110

Offset: 1

Author

Clark Kimberling, Apr 30 2019

Keywords

• nonn
• easy

Examples

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

Links

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

Crossrefs

Cf. A325417, A325430.

Programs

Mathematica

a = {1}; Do[AppendTo[a, NestWhile[# + 1 &, Last[a] + 1, Apply[Or,
Map[MemberQ[a, #] &, Select[Flatten[{#/3,
If[Mod[#, 3] == 0, (2 #)/3, 0] + If[Mod[#, 3] == 1, 1/3 (1 + 2 #), 0]}],
IntegerQ || # == 0]]] &]], {150}]; a  (* A325429 *)
Complement[Range[Last[a]], a]         (* A325430 *)
(* Peter J. C. Moses, Apr 25 2019 *)