The OEIS is supported by the many generous donors to the OEIS Foundation.

 Year-end appeal: Please make a donation to the OEIS Foundation to support ongoing development and maintenance of the OEIS. We are now in our 59th year, we have over 358,000 sequences, and we’ve crossed 10,300 citations (which often say “discovered thanks to the OEIS”). Other ways to Give
 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 A118369 Numbers k such that 1 + Product_{d|k} d is prime. 10
 1, 2, 6, 10, 14, 24, 26, 54, 56, 74, 88, 94, 134, 146, 154, 174, 206, 238, 248, 266, 296, 314, 326, 328, 374, 378, 386, 430, 442, 466, 472, 488, 494, 498, 510, 568, 582, 584, 634, 674, 680, 710, 730, 742, 786, 856, 874, 894, 918, 962, 986, 1038, 1094, 1174 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS See A118370 for the corresponding primes, 'divisorial primes'. LINKS Paolo P. Lava, Table of n, a(n) for n = 1..10000 EXAMPLE The (positive) divisors of 6 are 1,2,3,6. As 6*3*2*1 + 1 = 37 is prime, 6 is a term. MATHEMATICA f[n_]:=PrimeQ[Times@@Divisors[n]+1]; lst={}; Do[If[f[n], AppendTo[lst, n]], {n, 7!}]; lst (* Vladimir Joseph Stephan Orlovsky, Dec 14 2009 *) PROG (PARI) for(n=1, 2500, s=1; fordiv(n, d, s=s*d); if(isprime(s+1), print1(n, ", "))) CROSSREFS Cf. A118370, A007955. Sequence in context: A192109 A216090 A342641 * A226829 A236423 A082816 Adjacent sequences: A118366 A118367 A118368 * A118370 A118371 A118372 KEYWORD nonn AUTHOR Rick L. Shepherd, Apr 25 2006 STATUS approved

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

Last modified December 7 05:41 EST 2022. Contains 358649 sequences. (Running on oeis4.)