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%I #21 Sep 07 2017 09:27:49
%S 4,9,21,49,65,86,265,1081,1897,2513,7739,97229,128801,299426,922111,
%T 1221537,2839729,62608681,338356945,53406819691,2066337330754,
%U 6363483400447,8429820731201,432062194544201,7190854504969591,12619069972000553,16716708595637087
%N Padovan numbers that are semiprimes.
%C The smallest candidate for the next term in the b-file is A000931(1958), which is composite with 239 digits and an unknown number of prime factors. - _Hugo Pfoertner_, Sep 07 2017
%H Hugo Pfoertner, <a href="/A122498/b122498.txt">Table of n, a(n) for n = 1..54</a>
%H Eric Weisstein's World of Mathematics, <a href="http://mathworld.wolfram.com/Semiprime.html">Semiprime</a>
%p select(x-> numtheory[bigomega](x)=2, [(<<0|1|0>,
%p <0|0|1>, <1|1|0>>^i)[1$2]$i=0..300])[]; # _Alois P. Heinz_, Aug 31 2017
%t SemiprimeQ[1] := False SemiprimeQ[n_Integer] := Plus @@ (Last /@ FactorInteger[n]) == 2 a = Table[ SeriesCoefficient[ Series[x/(1 - x^2 - x^3), {x, 0, 50}], n], {n, 0, 50}] f[n_] = If[SemiprimeQ[a[[n]]] == True, a[[n]], {}] Flatten[Table[f[n], {n, 1, Length[a]}]]
%Y Cf. A000931, A001358, A053409, A100891.
%K nonn
%O 1,1
%A _Roger L. Bagula_, Sep 15 2006
%E More terms from _Alois P. Heinz_, Aug 31 2017
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