A101636 a(n) = least odd prime p such that (p^(P(n))-1)/(p-1) is prime with P(i) = i-th prime, n>1.

3, 7, 3, 5, 3, 11, 11, 113, 151, 19, 61, 53, 89, 5, 307, 19, 19, 491, 3, 11, 271, 41, 251, 271, 359, 3, 19, 79, 233, 5, 7, 13, 11, 5, 29, 71, 139, 127, 139, 2003, 5, 743, 673, 593, 383, 653, 661, 251, 6389, 2833, 223, 163, 37, 709, 131, 41, 2203, 941, 2707, 13, 1283

Offset

2,1

Comments

All primes certified using PRIMO.

Links

Table of n, a(n) for n=2..62.

Example

(3^3-1)/2=26/2=13 prime so for P(2) a(2)=3.

Mathematica

a = {}; Do[ p1 = Prime[n]; k = 2; While[p2 = Prime[k]; ! PrimeQ[(p2^p1 - 1)/(p2 - 1)], k++ ]; AppendTo[a, p2]; , {n, 2, 62}]; a (* Ray Chandler, Jan 27 2005 *)
f[n_] := Block[{P = Prime[n], k = 2}, While[p = Prime[k]; !PrimeQ[(p^P - 1)/(p - 1)], k++ ]; Prime[ k]]; Table[ f[n], {n, 2, 62}] (* Robert G. Wilson v, Jan 27 2005 *)

Prog

(PARI) a(n) = my(p=3, q=prime(n)); while (!ispseudoprime((p^q-1)/(p-1)), p=nextprime(p+1)); p; \\ Michel Marcus, Mar 21 2023

Crossrefs

Sequence in context: A132821 A247217 A252734 * A193534 A096247 A337013

Adjacent sequences: A101633 A101634 A101635 * A101637 A101638 A101639

Keyword

nonn

Author

Pierre CAMI, Jan 26 2005

Extensions

Extended by Ray Chandler and Robert G. Wilson v, Jan 27 2005

Status

approved