A258043 Smallest k such that prime(k)^n - 2 is prime.

3, 1, 8, 2, 2, 2, 4, 4, 2, 16, 193, 4, 8, 3, 4, 21, 11, 18, 8, 8, 11, 2, 8, 7, 70, 3, 95, 4, 172, 7, 4, 94, 143, 90, 193, 17, 2, 8, 46, 41, 2, 10, 254, 90, 74, 75, 371, 85, 70, 3, 177, 53, 85, 91, 18, 24, 84, 103, 34, 95, 34, 111, 80, 253, 84, 224, 397, 1002, 11, 33, 773, 29, 647, 20

Offset

1,1

Comments

Primes of the form prime(n)^n - 2: 3, 7, 61, 67, 71, 73, 127, ...

Links

Table of n, a(n) for n=1..74.

Example

a(1) = 3 because prime(3)^1 - 2 = 3 and 3 is prime,
a(2) = 1 because prime(1)^2 - 2 = 2 and 2 is prime,
a(3) = 8 because prime(8)^3 - 2 = 6857 and 6857 is prime.

Prog

(PARI) a(n) = my(k = 1); while(! isprime(prime(k)^n-2), k++); k; \\ Michel Marcus, May 23 2015

Crossrefs

Cf. A014224, A014232, A109080, A204578.

Sequence in context: A112420 A010288 A143291 * A200064 A242072 A248584

Adjacent sequences: A258040 A258041 A258042 * A258044 A258045 A258046

Keyword

nonn

Author

Juri-Stepan Gerasimov, May 22 2015

Status

approved