A181522 - OEIS

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

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OFFSET

1,3

LINKS

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

EXAMPLE

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

PROG

(Haskell)

import Data.List (subsequences)

a181522 = length . filter ((== 1) . a064911 . sum) .

subsequences . enumFromTo 1