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