A181522 Number of subsets of {1,2,...,n} whose sum is semiprime (cf. A001358, A064911).

0, 0, 2, 6, 13, 25, 47, 92, 184, 367, 721, 1416, 2769, 5407, 10662, 21135, 41866, 83220, 166617, 334852, 670725, 1334868, 2650263, 5280475, 10567613, 21145411, 42103939, 83382359, 164843079, 326791838, 650995628, 1301718424, 2605360702, 5205671338, 10369588530

Offset: 1

Author

Reinhard Zumkeller, Oct 27 2010

Keywords

• nonn

Examples

			a(4) = #{{1,3}, {4}, {1,2,3}, {2,4}, {2,3,4}, {1,2,3,4}} = 6.
		

Links

• Alois P. Heinz, Table of n, a(n) for n = 1..400

Crossrefs

Cf. A127542, A126024.

Cf. A064911.

Programs

Haskell

import Data.List (subsequences)
a181522 = length . filter ((== 1) . a064911 . sum) .
                          subsequences . enumFromTo 1
-- Reinhard Zumkeller, Feb 22 2012, Oct 27 2010