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 A189763 #4 Mar 30 2012 17:22:58 %S A189763 12,16,24,32,44,48,56,60,68,72,80,92,96,108,112,120,124,128,140,152, %T A189763 156,162,164,168,176,188,192,212,216,220,236,240,244,248,252,272,284, %U A189763 288,296,316,318,320,324,332,336,350,356,360,368,378,380,384,392,408 %N A189763 Even numbers n such that solutions to x' = n are not all semiprimes, where x' denotes the arithmetic derivative (A003415). %C A189763 It appears that the anti-derivatives of even numbers n are overwhelmingly semiprimes of the form (n/2)^2 - k^2. For example, 1000 has 28 anti-derivatives, all semiprimes. %Y A189763 Cf. A003415, A189762, A189764. %K A189763 nonn %O A189763 1,1 %A A189763 _T. D. Noe_, Apr 27 2011