A081313 Numbers having more than one representation as sum of a prime and a 3-smooth number.

4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 25, 26, 27, 29, 30, 31, 32, 33, 34, 35, 37, 38, 39, 40, 41, 43, 44, 45, 46, 47, 49, 50, 51, 53, 55, 56, 57, 59, 61, 62, 63, 64, 65, 67, 68, 69, 70, 71, 73, 74, 75, 76, 77, 79, 80, 81, 82, 83, 84, 85, 86

Offset: 1

Author

Reinhard Zumkeller, Mar 17 2003

Keywords

• nonn

Links

• Reinhard Zumkeller, Table of n, a(n) for n = 1..10000

Crossrefs

Cf. A000040, A003586, A081308, A081312.

Subsequence of A081311.

Programs

Haskell

a081313 n = a081313_list !! (n-1)
a081313_list = filter ((> 1) . a081308) [1..]
-- Reinhard Zumkeller, Jul 04 2012

Mathematica

nmax = 1000;
S = Select[Range[nmax], Max[FactorInteger[#][[All, 1]]] <= 3 &];
A081308[n_] := Count[TakeWhile[S, # < n &], s_ /; PrimeQ[n - s]];
Select[Range[nmax], A081308[#] > 1 &] (* Jean-François Alcover, Oct 13 2021 *)

Formula

A081308(a(n)) > 1.