The OEIS Foundation is supported by donations from users of the OEIS and by a grant from the Simons Foundation.

 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 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 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

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recent
The OEIS Community | Maintained by The OEIS Foundation Inc.

Last modified September 22 17:39 EDT 2021. Contains 347607 sequences. (Running on oeis4.)