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a(n) is the least number not 2*a(m)-1 or 3*a(m)-1 for any m < n.
4

%I #5 May 02 2019 16:03:57

%S 1,3,4,6,9,10,12,13,14,15,16,18,20,21,22,24,28,30,32,33,34,36,37,40,

%T 42,45,46,48,49,50,51,52,54,56,57,58,60,61,64,66,68,69,70,72,74,75,76,

%U 77,78,80,81,82,84,85,86,87,88,90,92,93,94,96,100,102,104

%N a(n) is the least number not 2*a(m)-1 or 3*a(m)-1 for any m < n.

%H Clark Kimberling, <a href="/A325440/b325440.txt">Table of n, a(n) for n = 1..10000</a>

%e 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 5 and 8 are disallowed, and a(3) = 4. See A325417 for a guide to related sequences.

%t a = {1}; Do[AppendTo[a, NestWhile[# + 1 &, Last[a] + 1, Apply[Or,

%t Map[MemberQ[a, #] &, Select[Flatten[{(#+1)/2, (#+1)/3}],

%t IntegerQ]]] &]], {150}]; a (* A325440 *)

%t Complement[Range[Last[a]], a] (* A325441 *)

%t (* _Peter J. C. Moses_, Apr 25 2019 *)

%Y Cf. A325417, A325441.

%K nonn,easy

%O 1,2

%A _Clark Kimberling_, May 02 2019