OFFSET
1,1
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
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