cp's OEIS Frontend

This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.

Showing 1-2 of 2 results.

A051896 a(n) = smallest palindrome > a(n-1) such that a(1)*a(2)*...*a(n) + 1 is prime with a(1) = 2.

Original entry on oeis.org

2, 3, 5, 6, 9, 55, 66, 77, 88, 161, 191, 313, 484, 494, 525, 747, 3223, 3993, 11711, 13431, 13731, 18881, 19691, 21012, 21112, 22422, 24242, 34443, 35353, 41114, 44244, 44844, 46664, 52225, 52925, 53935, 58385, 59895, 60806, 64146, 71917
Offset: 1

Views

Author

Felice Russo, Dec 21 1999

Keywords

Crossrefs

Subsequence of A002113.

Programs

  • Mathematica
    nxt[{t_,a_}]:=Module[{k=a+1},While[(!PalindromeQ[k])||CompositeQ[k*t+1],k++];{t*k,k}]; NestList[nxt,{2,2},40][[All,2]] (* Harvey P. Dale, Apr 18 2022 *)

Extensions

Initial conditions added to description by Chai Wah Wu, Apr 16 2021

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.

Original entry on oeis.org

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

Views

Author

Felice Russo, Dec 21 1999

Keywords

Crossrefs

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
Showing 1-2 of 2 results.