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Products of distinct Narayana's cow numbers (A000930).
2

%I #10 Feb 08 2020 11:31:04

%S 2,3,4,6,8,9,12,13,18,19,24,26,27,28,36,38,39,41,48,52,54,56,57,60,72,

%T 76,78,82,84,88,104,108,112,114,117,120,123,129,144,152,156,162,164,

%U 168,171,176,180,189,216,224,228,234,240,246,247,252,258,264,277

%N Products of distinct Narayana's cow numbers (A000930).

%H Clark Kimberling, <a href="/A274452/b274452.txt">Table of n, a(n) for n = 1..10000</a>

%e The Narayana's cow numbers numbers are 1, 2, 3, 4, 6, 9, 13, 19, 28, ..., so that the sequence of all products of distinct members, in increasing order, is (2, 3, 4, 6, 8, 9, 12, 13, 18, 19, 24, ...).

%t r[1] := 1; r[2] := 1; r[3] = 1; r[n_] := r[n] = r[n - 1] + r[n - 3]

%t s = {1}; z = 60; f = Map[r, Range[z]]; Take[f, 20] (*A000930*)

%t Do[s = Union[s, Select[s*f[[i]], # <= f[[z]] &]], {i, z}];

%t Take[s, 2 z] (* A274452 *)

%Y Cf. A160009, A274280, A274432.

%K nonn,easy

%O 1,1

%A _Clark Kimberling_, Jun 23 2016