A237759 Numbers n such that either n^2*2^n-1 or n^2*2^n+1 is prime, but not both.

1, 2, 4, 7, 21, 25, 30, 33, 41, 45, 57, 63, 83, 100, 131, 142, 144, 147, 150, 175, 198, 225, 304, 425, 449, 469, 513, 651, 782, 858, 1345, 1839, 1883, 1913, 2177, 2551, 2907, 3638, 3675, 6071, 6076, 9297, 11037, 11743, 12135, 12876, 14641, 38685, 40857

Offset

1,2

Links

Table of n, a(n) for n=1..49.

Example

4 is in the sequence because 4^2*2^4 - 1 = 16*16 - 1 = 255 is not a prime number but 4^2*2^4 + 1 = 16*16 + 1 = 257 is a prime number.

Prog

(PARI) isok(n) = isp1 = isprime(2^n*n^2-1); isp2 = isprime(2^n*n^2+1); (isp1 || isp2 && !(isp1 && isp2)); \\ Michel Marcus, Mar 05 2014

Crossrefs

Cf, A058781, A058780.

Sequence in context: A101805 A145777 A188497 * A306978 A337062 A153550

Adjacent sequences: A237756 A237757 A237758 * A237760 A237761 A237762

Keyword

nonn,less

Author

Juri-Stepan Gerasimov, Feb 24 2014

Extensions

Corrected by R. J. Mathar, Feb 26 2014

Status

approved