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%I #13 Jul 15 2022 10:35:15
%S 4,15,84,210,2002,5005,116280,319770,2042975,5311735,193536720,
%T 548354040,1476337800,9669554100,25140840660,991493848554,
%U 6499270398159,27900908274925,280576272201225,1210269541711230,3342649210440540,34315056105966195,227068876035237600,2305629203680278840
%N a(n) = binomial(s(n), n) where s(n) = n-th semiprime.
%C Semiprime analog of A060604.
%H Harvey P. Dale, <a href="/A117927/b117927.txt">Table of n, a(n) for n = 1..1000</a>
%F a(n) = binomial(A001358(n), n).
%e a(1) = binomial(4,1) = 4.
%e a(2) = binomial(6,2) = 15.
%e a(3) = binomial(9,3) = 84.
%e a(4) = binomial(10,4) = 210.
%e a(5) = binomial(14,5) = 2002.
%e a(6) = binomial(15,6) = 5005.
%e a(7) = binomial(21,7) = 116280.
%e a(8) = binomial(22,8) = 319770.
%e a(9) = binomial(25,9) = 2042975.
%e a(10) = binomial(26,10) = 5311735.
%t Binomial[First[#],Last[#]]&/@With[{sprs=Select[Range[70],PrimeOmega[#] == 2&]},Thread[{sprs,Range[Length[sprs]]}]] (* _Harvey P. Dale_, Aug 10 2012 *)
%o (PARI) s(n) = my(k=1, nb=0); while (nb != n, if (bigomega(k)==2, nb++); if (nb != n, k++)); k; \\ A001358
%o a(n) = binomial(s(n), n); \\ _Michel Marcus_, Jul 15 2022
%Y Cf. A001358, A060604.
%K easy,nonn
%O 1,1
%A _Jonathan Vos Post_, May 03 2006
%E More terms from _Michel Marcus_, Jul 15 2022
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