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

Author

Yasutoshi Kohmoto

Keywords

• nonn

Links

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

Crossrefs

Cf. A031441.

Programs

Mathematica

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

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