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

Offset: 1

Author

Jonathan Vos Post, Feb 23 2010

Keywords

• nonn

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.

Examples

			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.

Formula

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