OFFSET
1,1
COMMENTS
It is known that divisors of M(p)=2^p-1 are of the form 2kp+1. For k=1, these are the Lucasian primes A002515, for k=2 there are no such divisors, for k=3 these divisors are listed in A188130 and for k=4 in A122095.
The equivalent sequence of prime indices is 14, 93, 101, 105, 153, 232, 261, 269, ....
If k == 2 (mod 4), there are no such divisors in general and here there are no smaller k's than k = 5. - Karl-Heinz Hofmann, Jan 27 2022
LINKS
Amiram Eldar, Table of n, a(n) for n = 1..10000
FORMULA
MATHEMATICA
Select[Range[2*10^4], PrimeQ[#] && PowerMod[2, #, 10# + 1] == 1 &] (* Amiram Eldar, Nov 13 2019 *)
PROG
(PARI) forprime(p=1, 1e5, Mod(2, p*10+1)^p-1 | print1(p", "))
(Python) from sympy import sieve
print([p for p in sieve[1:10000] if pow(2, p, 10*p+1) == 1])
# Karl-Heinz Hofmann, Jan 27 2022
CROSSREFS
KEYWORD
nonn
AUTHOR
M. F. Hasler, Mar 21 2011
STATUS
approved