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 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

%I

%S 1,2,6,36,360,6480,220320,14541120,1890345600,487709164800,

%T 250682510707200,257200255985587200,527260524770453760000,

%U 2160713630509319508480000,17704887488393364052485120000

%N 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}.

%F a(n)=(2^(n-2)+2)*a(n-1), n>3. - _Vladeta Jovovic_, Nov 17 2003

%e 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.

%Y Cf. A089985.

%K nonn

%O 1,2

%A _Amarnath Murthy_, Nov 14 2003

%E More terms from _Ray Chandler_, Nov 21 2003

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Last modified September 22 17:26 EDT 2021. Contains 347607 sequences. (Running on oeis4.)