A081980 a(n) = numerator of the sum of the reciprocals of the n primes from prime(n(n-1)/2+1) to prime(n(n+1)/2).

1, 8, 311, 40808, 12185065, 6287341056, 4738802232119, 5387114456064096, 8850391860017878609, 18339240151336533115830, 44718225006409477834272143, 173879507464360746581828003860

Offset

1,2

Comments

Sum of all possible products of taking n-1 primes out of next n primes.

Links

Table of n, a(n) for n=1..12.

Mathematica

a[n_] := Numerator[Sum[1/Prime[i], {i, n(n-1)/2+1, n(n+1)/2}]]

Crossrefs

Sequence in context: A193812 A222095 A231124 * A264661 A231781 A220618

Adjacent sequences: A081977 A081978 A081979 * A081981 A081982 A081983

Keyword

nonn

Author

Amarnath Murthy, Apr 04 2003

Extensions

More terms from Antonio G. Astudillo (afg_astudillo(AT)lycos.com), Apr 08 2003

Status

approved