OFFSET
1,1
COMMENTS
a(n) is equal to 1 or a safe prime p: (p-1)/2 is also prime, A005385[n] = 5,7,11,23,47,59,83,107,167,179,227,263,347,359,383,467,479,503,563,587,719,839,863,887,983,1019... The indices of primes in a(n) are n=1,2,3,5,9,10,13,16,23,24..=A072192[n] Indices of Sophie Germain primes: p and 2p+1 are primes.
FORMULA
a(n) = Denominator[BernoulliB[2Prime[n]]]/6.
MATHEMATICA
Table[Denominator[BernoulliB[2Prime[n]]]/6, {n, 1, 100}]
CROSSREFS
KEYWORD
nonn
AUTHOR
Alexander Adamchuk, Jul 28 2006
STATUS
approved