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 A181522 Number of subsets of {1,2,...,n} whose sum is semiprime (cf. A001358, A064911). 3
 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 (list; graph; refs; listen; history; text; internal format)
 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 -- Reinhard Zumkeller, Feb 22 2012, Oct 27 2010 CROSSREFS Cf. A127542, A126024. Cf. A064911. Sequence in context: A065220 A048094 A335439 * A031872 A259577 A172348 Adjacent sequences:  A181519 A181520 A181521 * A181523 A181524 A181525 KEYWORD nonn AUTHOR Reinhard Zumkeller, Oct 27 2010 STATUS approved

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Last modified January 26 19:45 EST 2021. Contains 340442 sequences. (Running on oeis4.)