login
This site is supported by donations to The OEIS Foundation.

 

Logo

Please make a donation to keep the OEIS running. We are now in our 55th year. In the past year we added 12000 new sequences and reached 8000 citations (which often say "discovered thanks to the OEIS"). We need to raise money to hire someone to manage submissions, which would reduce the load on our editors and speed up editing.
Other ways to donate

Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A131409 Middle of three subsequent 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.

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

STATUS

approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recent
The OEIS Community | Maintained by The OEIS Foundation Inc.

License Agreements, Terms of Use, Privacy Policy. .

Last modified December 7 05:14 EST 2019. Contains 329839 sequences. (Running on oeis4.)