OFFSET
1,1
COMMENTS
a(7) > 13. See A240747 for more information.
a(n) is also the n-values such that A240747(n) is nonzero.
It is known that a(n) == 1 mod 4 or 2 mod 4 (except a(2) = 4).
If n is not squarefree, then n is not a member of this sequence.
It is known that 17, 22, 30, 41, 66, and 194 are members of this sequence.
EXAMPLE
There are primes of the form 2^k-1 (A000043) so 2 is a member of this sequence.
PROG
(PARI) s(n) = for(k=1, 6000, if(ispseudoprime(n^k-sum(i=1, n-1, i^k)), return(k)))
n=1; while(n<200, if(s(n), print(n)); n+=1)
CROSSREFS
KEYWORD
nonn,more,hard
AUTHOR
Derek Orr, Apr 11 2014
STATUS
approved