A082021 a(0) = 7; for n > 0, a(n) is the greatest prime factor of PP(PP(a(n-1)))*a(n-1)+2 where PP(n) is an abbreviation for PreviousPrime(n).

7, 23, 131, 47, 643, 2459, 2000807, 503347241, 82125909539251, 9617692012399, 55555555342491359799151, 1116817987709786226917069, 578610396154837, 66992050984853, 254497141, 1660738053545999, 201525986561, 25600818891233, 796725607788661087, 23547857117470471

Offset: 0

Author

Yasutoshi Kohmoto, May 10 2003

Keywords

• nonn

Links

• Tyler Busby, Table of n, a(n) for n = 0..25

Crossrefs

Cf. A082032, A031441, A031442.

Programs

Mathematica

NestWhileList[FactorInteger[2+#*Prime[PrimePi[ # ]-2]][[ -1,1]] &, 7, True, 8] (* T. D. Noe, Nov 15 2006 *)
NestList[FactorInteger[NextPrime[NextPrime[#,-1],-1]#+2][[-1,1]]&,7,20] (* Harvey P. Dale, Dec 26 2017 *)

Extensions

Description corrected by Rick L. Shepherd, Dec 19 2004

Corrected by T. D. Noe, Nov 15 2006

More terms from Harvey P. Dale, Dec 26 2017

a(19) from Tyler Busby, Oct 12 2023