A031442 a(0) = 13; for n > 0, a(n) is the greatest prime factor of PreviousPrime(a(n-1))*a(n-1)-1 where PreviousPrime(prime(k))=prime(k-1).

13, 71, 41, 379, 23561, 5431, 20269, 89, 1231, 44497, 329952671, 36583, 1126159, 90209117, 14095897, 15272393, 13887359, 256460794943, 2740505805180429880723, 1591234463080874838018721796071210709

Offset

0,1

Links

Tyler Busby, Table of n, a(n) for n = 0..21

Mathematica

NestList[FactorInteger[#*NextPrime[#, -1]-1][[-1, 1]]&, 13, 20] (* Harvey P. Dale, May 26 2025 *)

Crossrefs

Cf. A031441.

Sequence in context: A050403 A235454 A296831 * A066831 A067382 A340842

Adjacent sequences: A031439 A031440 A031441 * A031443 A031444 A031445

Keyword

nonn

Author

Yasutoshi Kohmoto

Extensions

More terms from Kok Seng Chua (chuaks(AT)ihpc.nus.edu.sg), May 23 2000. a(19) and a(20) pass the strong pseudoprime test for many bases.

Edited by T. D. Noe, Oct 30 2008

Status

approved