A002255 Numbers k such that 7*4^k + 1 is prime.

1, 2, 3, 7, 10, 13, 25, 26, 46, 60, 87, 90, 95, 145, 160, 195, 216, 308, 415, 902, 1128, 3307, 6748, 7747, 8348, 11193, 27243, 44033, 47665, 103542, 141517, 280908, 402267, 405615, 745926, 1069956, 1083900, 1457977, 1507881, 1755887

Offset: 1

Author

N. J. A. Sloane

Keywords

• hard
• nonn

References

• H. Riesel, Prime numbers and computer methods for factorization, in Progress in Mathematics, Vol. 57, Birkhauser, Boston, 1985, Chap. 4, see pp. 381-384.
• N. J. A. Sloane, A Handbook of Integer Sequences, Academic Press, 1973 (includes this sequence).
• N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).

Links

• Ray Ballinger, Proth Search Page.
• C. K. Caldwell, The Prime Pages.
• R. K. Guy, The strong law of small numbers. Amer. Math. Monthly 95 (1988), no. 8, 697-712. [Annotated scanned copy]
• R. M. Robinson, A report on primes of the form k.2^n+1 and on factors of Fermat numbers, Proc. Amer. Math. Soc., 9 (1958), 673-681.
• Index entries for sequences of n such that k*2^n-1 (or k*2^n+1) is prime

Crossrefs

See A032353 (which is the main entry for this sequence) for more terms.

Programs

PARI

is(n)=ispseudoprime(7*4^n+1) \\ Charles R Greathouse IV, Jun 06 2017

Extensions

More terms (from A032353) added by Joerg Arndt, Apr 07 2013