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%I #16 Nov 21 2013 12:50:07
%S 4,10,46,85,166,235,274,361,514,694,901,1135,1219,1306,1585,1891,2461,
%T 2839,3106,3385,3826,3979,4135,5311,5674,6049,6241,6835,7246,8551,
%U 9481,10966,11485,11749,12286,12559,13969,15151,15454,17335,18649,18985,19666,21421,21781,22879,23626,24385,26734,27949,28774,30034,32194,33079,33526
%N Semiprime centered triangular numbers.
%C Numbers of the form 3*n*(n-1)/2 + 1 = p*q where p and q are primes, not necessarily distinct. This is to semiprimes A001358 as A125602 is to primes A000040.
%F A001358 INTERSECTION A005448.
%e a(3) = 3*6(6-1)/2 + 1 = 10 = 2 * 5.
%t SemiprimeQ[n_] := Total[FactorInteger[n]][[2]] == 2; Select[Table[3*n (n - 1)/2 + 1, {n, 150}], SemiprimeQ]
%t Select[Table[(3n(n-1))/2+1,{n,200}],PrimeOmega[#]==2&] (* _Harvey P. Dale_, May 13 2012 *)
%Y Cf. A001358, A005448, A125602.
%K nonn,easy
%O 1,1
%A _Jonathan Vos Post_, Feb 12 2011
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