OFFSET
1,2
COMMENTS
a(19) > 1062, if it exists. - Amiram Eldar, Jun 29 2021
LINKS
Peter Cameron, Between Fermat and Mersenne, Blog Post, October 07 2020.
Peter Cameron, Between Fermat and Mersenne, Blog Post, October 07 2020. [Local copy, with permission.]
Peter J. Cameron, Pallabi Manna, and Ranjit Mehatari, On finite groups whose power graph is a cograph, arXiv:2106.14217 [math.GR], 2021. See Theorem 1.3 (b) pp. 3-4.
EXAMPLE
2^13 = 8192, and 8191 is a prime and 8193 = 3*2731 is the product of twop primes, so 13 is a term. - N. J. A. Sloane, Nov 01 2024
PROG
(PARI) isor(q) = (q==1) || isprimepower(q) || (bigomega(q)==2);
isokb(d) = my(q=2^d); isor(q-1) && isor(q+1);
CROSSREFS
KEYWORD
nonn,hard,more,changed
AUTHOR
Michel Marcus, Jun 29 2021
EXTENSIONS
a(18) from Amiram Eldar, Jun 29 2021
STATUS
approved