OFFSET
1,1
COMMENTS
The only composite in this sequence is a(2) = 217 = 7*31. All other a(n) are equal to 1 (for n=3,7,12,15,17,18,19,20,21,22,26,28,31,33,34,35,38,39,45,46..) or prime: a(1) = 5, all other primes in a(n) belong to A068231[n]: Primes congruent to 11 (mod 12). It appears that every prime from A068231[n] except 11 shows up in a(n) just once.
LINKS
Vincenzo Librandi, Table of n, a(n) for n = 1..500
FORMULA
a(n) = Denominator[BernoulliB[10Prime[n]]]/66.
MATHEMATICA
Table[Denominator[BernoulliB[10Prime[n]]]/66, {n, 1, 47}]
CROSSREFS
KEYWORD
nonn
AUTHOR
Alexander Adamchuk, Jul 28 2006
STATUS
approved