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 A113784 #9 Jul 11 2015 10:31:52 %S A113784 5,4,5,5,7,7,4,4,8,8,2,4,4,8,10,5,6,6,3,5,7,7,9,8,8,8,4,2,5,6,3,2,12, %T A113784 16,9,7,4,3,3,2,7,10,5,8,8,2,3,3,10,12,4,3,7,8,11,9,6,7,4,9,14,8,2,3, %U A113784 3,4,7,5,2,3,3,2,3,7,14,11,12,12,6,5,6,8,6,5,9,11,13,11,4,6,7,4,3,3,2,3,6,9 %N A113784 Difference between semiprime(n) and semiprime(n+2). %C A113784 Semiprime analog of A031131 "Difference between n-th prime and (n+2)nd prime." %F A113784 a(n) = A001358(n+2) - A001358(n). %e A113784 a(1) = 5 because 3rd semiprime - first semiprime = 9 - 4 = 5. %e A113784 a(2) = 4 because semiprime(4) - semiprime(2) = 10 - 6 = 4. %e A113784 a(3) = 5 because semiprime(5) - semiprime(3) = 14 - 9 = 5. %e A113784 a(4) = 5 because semiprime(6) - semiprime(4) = 15 - 10 = 5. %t A113784 t = Select[ Range@320, Plus @@ Last /@ FactorInteger@# == 2 &]; Drop[t, 2] - Drop[t, -2] (* _Robert G. Wilson v_ *) %Y A113784 Cf. A001358, A056809. %K A113784 easy,nonn %O A113784 1,1 %A A113784 _Jonathan Vos Post_, Jan 20 2006 %E A113784 More terms from _Robert G. Wilson v_, Jan 21 2006