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

Author

Jonathan Vos Post, Apr 23 2010

Keywords

• easy
• nonn

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.

Examples

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

Crossrefs

Cf. A000110, A058681.

Programs

Mathematica

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

Formula

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