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A236068 Primes p such that f(f(p)) is prime, where f(x) = x^2 + 1. 0
3, 5, 13, 43, 47, 127, 263, 277, 293, 337, 347, 397, 443, 467, 487, 503, 577, 593, 607, 673, 727, 733, 773, 857, 887, 907, 1153, 1427, 1487, 1567, 1583, 1637, 1777, 2003, 2213, 2243, 2477, 2503, 2557, 2633, 2687, 2777 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

LINKS

Table of n, a(n) for n=1..42.

FORMULA

a(n) = (A235053(n)-1)^(1/2).

EXAMPLE

47 is prime and (47^2+1)^2+1 is also prime. So, 47 is a member of this sequence.

PROG

(Python)

import sympy

from sympy import isprime

{print(p) for p in range(10**4) if isprime(p) and isprime((p**2+1)**2+1)}

(PARI) isok(p) = isprime(p) && (q = p^2+1) && isprime(q^2+1); \\ Michel Marcus, Jan 19 2014

CROSSREFS

Cf. A235053.

Sequence in context: A188583 A259932 A178432 * A057188 A128548 A321358

Adjacent sequences:  A236065 A236066 A236067 * A236069 A236070 A236071

KEYWORD

nonn

AUTHOR

Michel Marcus and Derek Orr, Jan 19 2014

STATUS

approved

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Last modified January 25 01:49 EST 2020. Contains 331229 sequences. (Running on oeis4.)