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%I #12 Oct 15 2021 14:45:16
%S 4,49,55,91,119,143,159,183,185,203,215,219,235,247,265,287,289,299,
%T 303,319,321,327,339,391,411,413,415,451,469,471,515,517,527,533,535,
%U 543,551,579,581,589,667,669,679,685,687,695,721,753,779,789,791,813,815
%N Numbers n such that n and n+2 are consecutive semiprimes.
%H Zak Seidov, <a href="/A136196/b136196.txt">Table of n, a(n) for n = 1..1000.</a>
%e 4 and 6 are 1st and 2nd semiprimes,
%e 49 and 51 are 17th and 18th semiprimes,
%e 55 and 57 are 19th and 20th semiprimes.
%t Position[Partition[PrimeOmega[Range[900]],3,1],_?(#[[1]]==#[[3]]==2 && #[[2]]!=2&),1,Heads->False]//Flatten (* _Harvey P. Dale_, Oct 15 2021 *)
%o (PARI) isok(n) = (bigomega(n) == 2) && (bigomega(n+2) == 2) && (bigomega(n+1) != 2); \\ _Michel Marcus_, Oct 13 2013
%Y Cf. A001358, A065516.
%K nonn
%O 1,1
%A _Zak Seidov_, Dec 21 2007
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