A198196 Numbers k such that [V(4,1,k)/4] = floor(cosh(k log(sqrt(3)+2))/2) = A004526(A001075(k)) is a prime.

2, 3, 5, 7, 11, 13, 17, 19, 79, 151, 199, 233, 251, 317, 863, 971

Offset

1,1

Comments

Further terms are 3049, 7451, 7487, 18869.

All terms must be primes. A117808 lists the corresponding primes floor(A001075(k)/2). Actually, the "floor" here and in the definition is only needed for the initial term 2, since no other even (thus composite) k can be in the sequence, and A001075(k) is even for odd k.

Links

Table of n, a(n) for n=1..16.

D. Broadhurst, Re: Cubic factors of n^n+(n+1)^(n+1), in "primenumbers" Yahoo group, Oct 21 2011.

David Broadhurst, Cubic factors of n^n+(n+1)^(n+1), digest of 3 messages in primenumbers Yahoo group, Oct 21 - Oct 22, 2011.

Prog

(PARI) q=2+quadgen(12); for(n=1, 1e9, ispseudoprime(real(q^n)\2) & print1(n", "))

Crossrefs

Sequence in context: A088415 A175063 A248199 * A139054 A290959 A003309

Adjacent sequences: A198193 A198194 A198195 * A198197 A198198 A198199

Keyword

nonn,more

Author

M. F. Hasler, Oct 21 2011

Status

approved