A173761 - OEIS

A173761

Partial sums of A002861.

1, 3, 7, 16, 36, 87, 212, 541, 1403, 3714, 9931, 26880, 73230, 200944, 554216, 1535969, 4273508, 11933297, 33425583, 93891713, 264401743, 746269426, 2110694255, 5981068081, 16977958318, 48271041858

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OFFSET

1,2

COMMENTS

Partial sums of number of connected functions (or mapping patterns) on n unlabeled points, or number of rings and branches with n edges. The subsequence of primes in this partial sum begins: 3, 7, 9931, 1535969, 5981068081.

LINKS

Table of n, a(n) for n=1..26.

FORMULA

a(n) = SUM[i=1..n] A002861(i).

EXAMPLE

a(26) = 1 + 2 + 4 + 9 + 20 + 51 + 125 + 329 + 862 + 2311 + 6217 + 16949 + 46350 + 127714 + 353272 + 981753 + 2737539 + 7659789 + 21492286 + 60466130 + 170510030 + 481867683 + 1364424829 + 3870373826 + 10996890237 + 31293083540.

CROSSREFS

Cf. A002861, A000081, A001372.

Sequence in context: A020746 A033303 A078056 * A361507 A124671 A188626

Adjacent sequences: A173758 A173759 A173760 * A173762 A173763 A173764

KEYWORD

nonn

AUTHOR

Jonathan Vos Post, Feb 23 2010

STATUS

approved