A089709 a(1) = 1, a(2) = 2; for n>2, a(n) = sum_{r=1..n} {sum of all previous terms taken r at a time}.

1, 2, 6, 36, 360, 6480, 220320, 14541120, 1890345600, 487709164800, 250682510707200, 257200255985587200, 527260524770453760000, 2160713630509319508480000, 17704887488393364052485120000

Offset: 1

Author

Amarnath Murthy, Nov 14 2003

Keywords

• nonn
• easy

Examples

			a(4) = [{a(1)} + {a(2)} + {a(3)}] + [{a(1) + a(2)} + {a(1) + a(3)} + {a(2) + a(3)}] + [{a(1) + a(2) + a(3)}] = 36.
		

Crossrefs

Cf. A089985.

Formula

a(n)=(2^(n-2)+2)*a(n-1), n>3. - Vladeta Jovovic, Nov 17 2003

Extensions

More terms from Ray Chandler, Nov 21 2003