A176688 Partial sums of A058681.

1, 8, 44, 215, 1028, 5040, 25931, 141394, 818940, 5030489, 32670830, 223561960, 1606504121, 12086613500, 94951417768, 777028092855, 6609770035768, 58333927746852, 533203742855027, 5039919479205198, 49191925330095240

Offset

2,2

Comments

Partial sums of number of matroids of rank 2 on n labeled points. Partial sums of number of collections containing two or more nonempty subsets of {1,2,...n} that are pairwise disjoint. The subsequence of primes in this partial sum begins: 25931, 5030489.

Links

Table of n, a(n) for n=2..22.

Formula

a(n) = Sum_{i=2..n} A058681(i) = Sum_{i=2..n} (B(n+1) - 2^n), where B = Bell numbers (A000110).

Example

a(11) = 1 + 7 + 36 + 171 + 813 + 4012 + 20891 + 115463 + 677546 + 4211549 = 5030489 is prime.

Mathematica

Accumulate[Table[BellB[n+1]-2^n, {n, 2, 30}]] (* Harvey P. Dale, Feb 14 2012 *)

Crossrefs

Cf. A000110, A058681.

Sequence in context: A292487 A125318 A000373 * A272154 A270935 A197213

Adjacent sequences: A176685 A176686 A176687 * A176689 A176690 A176691

Keyword

easy,nonn

Author

Jonathan Vos Post, Apr 23 2010

Status

approved