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 A131409 Middle of three consecutive semiprimes with common prime factor = 3. 0
 3909, 87627, 132609, 163491, 167451, 170679, 209289, 224151, 270591, 309273, 318651, 327423, 340077, 395121, 444459, 481863, 497121, 522231, 536451, 584589, 624837, 633189, 680451, 752901, 765579, 767757, 830469, 848739, 878133, 915063, 938109, 953877, 954861 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS 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}. LINKS Table of n, a(n) for n=1..33. MATHEMATICA 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 *) PROG (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 CROSSREFS Sequence in context: A326385 A068240 A022212 * A209732 A221239 A136459 Adjacent sequences: A131406 A131407 A131408 * A131410 A131411 A131412 KEYWORD nonn AUTHOR Zak Seidov, Oct 01 2007 EXTENSIONS Duplicated term 340077 removed and more terms added by Michel Marcus, Oct 13 2013 Definition modified for clarity by Harvey P. Dale, Nov 15 2022 STATUS approved

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Last modified December 2 17:33 EST 2023. Contains 367525 sequences. (Running on oeis4.)