This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A181522 #9 Jan 21 2014 16:48:01
%S A181522 0,0,2,6,13,25,47,92,184,367,721,1416,2769,5407,10662,21135,41866,
%T A181522 83220,166617,334852,670725,1334868,2650263,5280475,10567613,21145411,
%U A181522 42103939,83382359,164843079,326791838,650995628,1301718424,2605360702,5205671338,10369588530
%N A181522 Number of subsets of {1,2,...,n} whose sum is semiprime (cf. A001358, A064911).
%H A181522 Alois P. Heinz, <a href="/A181522/b181522.txt">Table of n, a(n) for n = 1..400</a>
%e A181522 a(4) = #{{1,3}, {4}, {1,2,3}, {2,4}, {2,3,4}, {1,2,3,4}} = 6.
%o A181522 (Haskell)
%o A181522 import Data.List (subsequences)
%o A181522 a181522 = length . filter ((== 1) . a064911 . sum) .
%o A181522 subsequences . enumFromTo 1
%o A181522 -- _Reinhard Zumkeller_, Feb 22 2012, Oct 27 2010
%Y A181522 Cf. A127542, A126024.
%Y A181522 Cf. A064911.
%K A181522 nonn
%O A181522 1,3
%A A181522 _Reinhard Zumkeller_, Oct 27 2010