OFFSET
1,1
COMMENTS
Theorem: if n-1 is composite, then A090086(n) < n.
The inverse theorem is false iff n = p+1 for primes p in this sequence.
Conjecture: the sequence contains all sufficiently large primes. Probably all primes except 2, 3, 5, 7, 11, 13, 17, 19, 23, 29, 37, 41, 47, 53, 59, 71, 83, 89, 101, 109, 139, 149, 157, 179, 199, 307, 461, and 571.
EXAMPLE
The prime 31 is a term, since A090086(31+1) = 25 < 31.
PROG
(PARI) b(n) = {forcomposite(k=2, , if (Mod(n, k)^(k-1) == 1, return (k)); ); }
isok(p) = isprime(p) && (b(p+1) < p); \\ Michel Marcus, Aug 09 2018
CROSSREFS
KEYWORD
nonn
AUTHOR
Thomas Ordowski, Aug 09 2018
EXTENSIONS
Corrected and extended by Michel Marcus, Aug 09 2018
STATUS
approved