The OEIS Foundation is supported by donations from users of the OEIS and by a grant from the Simons Foundation.

Thanks to everyone who made a donation during our annual appeal!
To see the list of donors, or make a donation, see the OEIS Foundation home page.

 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 A108172 Semiprimes p*q where p is a prime of the form 6n+1 (A002476) and q is a prime of the form 6n-1 (A007528). 4
 35, 65, 77, 95, 119, 143, 155, 161, 185, 203, 209, 215, 221, 287, 299, 305, 323, 329, 335, 341, 365, 371, 377, 395, 407, 413, 437, 473, 485, 497, 515, 527, 533, 545, 551, 581, 611, 623, 629, 635, 671, 689, 695, 707, 713, 731, 737, 749, 755, 767, 779, 785 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS Also semiprimes of the form 6n-1 (or 6n+5). Every semiprime not divisible by 2 or 3 must be in one of these three disjoint sets: A108164 - the product of two primes of the form 6n+1 (A002476), A108166 - the product of two primes of the form 6n-1 (A007528), A108172 - the product of a prime of the form 6n+1 and a prime of the form 6n-1. The product of a prime of the form 6n+1 and a prime of the form 6n-1 is a semiprime of the form 6n-1. There are 740 of these numbers below 10,000. REFERENCES M. Abramowitz and I. A. Stegun, eds., Handbook of Mathematical Functions, National Bureau of Standards Applied Math. Series 55, 1964 (and various reprintings), p. 870. LINKS Vincenzo Librandi, Table of n, a(n) for n = 1..1000 M. Abramowitz and I. A. Stegun, eds., Handbook of Mathematical Functions, National Bureau of Standards, Applied Math. Series 55, Tenth Printing, 1972 [alternative scanned copy]. FORMULA a(n) = 6 * A112776(n) + 5. MATHEMATICA Select[Range[15, 1000, 2], Last/@FactorInteger[#]=={1, 1} && IntegerQ[(#-2)/3]&] (* Vladimir Joseph Stephan Orlovsky, May 07 2011 *) PROG (PARI) list(lim)=my(v=List(), t); forprime(p=5, lim\7, if(p%6<5, next); forprime(q=7, lim\5, if(q%6>1, next); t=p*q; if(t>lim, break); listput(v, t))); Set(v) \\ Charles R Greathouse IV, Feb 08 2017 CROSSREFS Cf. A001358, A002476, A007528, A190299. Sequence in context: A250764 A245274 A092256 * A176875 A292005 A331378 Adjacent sequences:  A108169 A108170 A108171 * A108173 A108174 A108175 KEYWORD easy,nonn AUTHOR Jonathan Vos Post, Jun 13 2005 EXTENSIONS Edited by Ray Chandler, Oct 15 2005 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.

Last modified January 17 23:37 EST 2020. Contains 330995 sequences. (Running on oeis4.)