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 A113883 #9 Jul 11 2015 10:32:37 %S A113883 4,6,16,31,33,49,84 %N A113883 Indices of semiprime Bell numbers A000110. %C A113883 Semiprime analog of A051130 (indices of prime Bell numbers). These indices of semiprime Bell numbers include all values through B(120), which has 146 digits and at least 5 prime factors, the smallest being 71. %H A113883 John Sokol, <a href="http://www.dnull.com/bells/bell1000.html">The First 1000 Bell Numbers</a>. %F A113883 n such that A000110(n) is semiprime. n such that A000110(n) is in A001358. %e A113883 a(1) = 4 because B(4) = 15 = 3 * 5. %e A113883 a(2) = 6 because B(6) = 203 = 7 * 29. %e A113883 a(3) = 16 because B(16) = 10480142147 = 241 * 43486067. %e A113883 a(4) = 31 because B(31) = 10293358946226376485095653 %e A113883 = 11 * 935759904202397862281423. %e A113883 a(5) = 33 because B(33) = 1629595892846007606764728147 %e A113883 = 5694673 * 286161451736738458339. %e A113883 a(6) = 49 because B(49) = %e A113883 10726137154573358400342215518590002633917247281 %e A113883 = 7615441337805454611187 * %e A113883 1408472165798904899327563. %e A113883 a(7) = 84 because B(84) is a 93-digit semiprime, whose smaller prime factor is 8429925224798761223. %Y A113883 Cf. A000110, A001358, A113015. %K A113883 easy,nonn %O A113883 1,1 %A A113883 _Jonathan Vos Post_, Jan 27 2006