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A131409 Middle of three consecutive semiprimes with common prime factor = 3. 0

%I #10 Nov 15 2022 17:25:27

%S 3909,87627,132609,163491,167451,170679,209289,224151,270591,309273,

%T 318651,327423,340077,395121,444459,481863,497121,522231,536451,

%U 584589,624837,633189,680451,752901,765579,767757,830469,848739,878133,915063,938109,953877,954861

%N Middle of three consecutive semiprimes with common prime factor = 3.

%C List of triples: {3903, 3909, 3921}, {87621, 87627, 87663}, {132603, 132609, 132621}, {163479, 163491, 163497}, {167439, 167451, 167457}, {170673, 170679, 170691}, {209283, 209289, 209301}, {224139, 224151, 224157}, {270573, 270591, 270597}, {309261, 309273, 309279}, {318639, 318651, 318657}, {327417, 327423, 327441}, {340071, 340077, 340089}, {395103, 395121, 395133}, {444453, 444459, 444471}, {481857, 481863, 481881}, {497109, 497121, 497127}, {522213, 522231, 522237}, {536439, 536451, 536457}, {584583, 584589, 584601}.

%t Select[Partition[{#,If[Divisible[#,3],1,0]}&/@Select[Range[10^6],PrimeOmega[ #] == 2&],3,1],#[[1,2]]==#[[2,2]]==#[[3,2]]==1&][[All,2,1]] (* _Harvey P. Dale_, Nov 15 2022 *)

%o (PARI) lista(nn) = {vec = vector(nn, i, i); sp = select(i->(bigomega(i) == 2), vec); for (i = 2, #sp-1, if (gcd(sp[i-1], gcd(sp[i], sp[i+1])) == 3, print1(sp[i], ", ")););} \\ _Michel Marcus_, Oct 13 2013

%K nonn

%O 1,1

%A _Zak Seidov_, Oct 01 2007

%E Duplicated term 340077 removed and more terms added by _Michel Marcus_, Oct 13 2013

%E Definition modified for clarity by _Harvey P. Dale_, Nov 15 2022

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Last modified March 29 07:27 EDT 2024. Contains 371265 sequences. (Running on oeis4.)