OFFSET
1,1
COMMENTS
Conjecture: sequence is infinite.
The only primes p such that p^11 - 1 has fewer than A309906(11)=8 divisors are 2 and 5.
p^11 - 1 = (p-1)*(p^10 + p^9 + p^8 + p^7 + p^6 + p^5 + p^4 + p^3 + p^2 + p + 1).
For every term p, p^11 - 1 is of the form 2*q*r, where q and r are distinct odd primes. With the exception of p=a(1)=3, each term p is a number such that (p-1)/2 and (p^10 + p^9 + p^8 + ... + p^2 + p + 1) are primes.
EXAMPLE
p =
n a(n) factorization of p^11 - 1
- ---- ------------------------------------------------
1 3 2 * 23 * 3851
2 467 2 * 233 * 494424256962371823779424877
3 2039 2 * 1019 * 1242754384106847037173120489949801
4 4679 2 * 2339 * 5030640462820574591105701447273296601
PROG
(PARI) isok(p) = isprime(p) && (numdiv(p^11-1) == 8); \\ Michel Marcus, Feb 28 2021
CROSSREFS
KEYWORD
nonn
AUTHOR
Jon E. Schoenfield, Feb 28 2021
STATUS
approved