A325427 a(n) is the least number not 2*a(m)+1 or floor(3*a(m)/2) for any m < n.

1, 2, 4, 7, 8, 11, 13, 14, 18, 20, 22, 24, 25, 26, 28, 31, 32, 34, 35, 38, 40, 43, 44, 47, 50, 54, 55, 56, 58, 59, 61, 62, 67, 68, 72, 73, 74, 76, 78, 79, 80, 83, 85, 86, 90, 92, 94, 96, 97, 98, 99, 103, 104, 105, 106, 107, 110, 112, 115, 116, 121, 122, 126

Offset

1,2

Links

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

Example

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 5 and 6 are disallowed, and a(3) = 4.  See A325417 for a guide to related sequences.

Mathematica

a = {1}; Do[AppendTo[a, NestWhile[# + 1 &, Last[a] + 1, Apply[Or,
Map[MemberQ[a, #] &, Select[Flatten[{(#-1)/2,
If[Mod[#, 3] == 0, (2 #)/3, 0] + If[Mod[#, 3] == 1, 1/3 (1 + 2 #), 0]}],
IntegerQ || # == 0]]] &]], {150}]; a  (* A325427 *)
Complement[Range[Last[a]], a]         (* A325428 *)
(* Peter J. C. Moses, Apr 25 2019 *)

Crossrefs

Cf. A325417, A325428.

Sequence in context: A238989 A093696 A190851 * A336656 A243751 A187838

Adjacent sequences: A325424 A325425 A325426 * A325428 A325429 A325430

Keyword

nonn,easy

Author

Clark Kimberling, Apr 30 2019

Status

approved