A051955 a(n) = smallest palindrome > a(n-1) such that a(1)*a(2)*...*a(n) + 1 and a(1)*a(2)*...*a(n) - 1 are primes.

4, 363, 434, 484, 494, 636, 4004, 46864, 47474, 135531, 695596, 1793971, 1826281, 1933391, 4700074, 4785874, 4806084, 6462646, 6574756, 9558559, 15399351, 46288264, 53500535, 57499475, 150787051, 185808581, 197636791, 226686622

Offset: 1

Author

Felice Russo, Dec 21 1999

Keywords

• nice
• nonn
• base

Crossrefs

Cf. A051896, A051954.

Subsequence of A002113.

Programs

Mathematica

a[1] = 4; a[n_] := a[n] = For[k = a[n-1]+1, True, k++, id = IntegerDigits[k]; If[id == Reverse[id], p = Product[a[j], {j, 1, n - 1}]*k + 1; If[PrimeQ[p] && PrimeQ[p-2], Return[k]]]]; Table[Print["a(", n, ") = ", a[n]]; a[n], {n, 1, 28}] (* Jean-François Alcover, Jul 30 2017 *)

Extensions

a(12)-a(28) from Donovan Johnson, Feb 17 2010