A175731 Semiprimes m such that either 2m-1 or 2m+1 is prime, but not both.

4, 10, 14, 22, 26, 33, 34, 35, 39, 49, 55, 57, 65, 74, 82, 86, 87, 91, 95, 106, 111, 115, 119, 121, 129, 134, 142, 146, 155, 158, 159, 166, 169, 177, 183, 187, 194, 201, 205, 209, 215, 217, 219, 221, 249, 254, 262, 274, 278, 289, 299, 301, 303, 323, 326, 327, 329, 339, 341

Offset

1,1

Links

Table of n, a(n) for n=1..59.

Example

a(1)=4 because 2*4-1=7=prime and 2*4+1=9=nonprime.

Prog

(PARI) isok(m) = (bigomega(m)==2) && bitxor(isprime(2*m-1), isprime(2*m+1)); \\ Michel Marcus, Feb 20 2023

Crossrefs

Intersection of A001358 and A174047.

Sequence in context: A161366 A310424 A176551 * A242486 A060031 A112825

Adjacent sequences: A175728 A175729 A175730 * A175732 A175733 A175734

Keyword

nonn

Author

Juri-Stepan Gerasimov, Aug 24 2010

Extensions

Corrected (15 removed) by R. J. Mathar, Aug 25 2010. Also corrected by D. S. McNeil.

Status

approved