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 A176688 Partial sums of A058681. 0
 1, 8, 44, 215, 1028, 5040, 25931, 141394, 818940, 5030489, 32670830, 223561960, 1606504121, 12086613500, 94951417768, 777028092855, 6609770035768, 58333927746852, 533203742855027, 5039919479205198, 49191925330095240 (list; graph; refs; listen; history; text; internal format)
 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 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. 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

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Last modified December 4 02:18 EST 2020. Contains 338921 sequences. (Running on oeis4.)