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

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

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 A396600 A221239

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