A082021 - OEIS

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

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OFFSET

0,1

LINKS

Tyler Busby, Table of n, a(n) for n = 0..22

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 *)

CROSSREFS

Cf. A082032, A031441, A031442.

Sequence in context: A064640 A064639 A064638 * A227254 A080082 A158954

Adjacent sequences: A082018 A082019 A082020 * A082022 A082023 A082024