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a(1)=1, a(n) = 2 * Sum_{k=1..n-1} (3^k-1)/2 * a(k) for n>=2.
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%I #20 Apr 02 2017 10:36:56

%S 1,2,10,140,5740,700280,255602200,279628806800,917462115110800,

%T 9029662136920493600,266600774592577573540000,

%U 23613897008762965998731960000,6274708327065504088149055143160000

%N a(1)=1, a(n) = 2 * Sum_{k=1..n-1} (3^k-1)/2 * a(k) for n>=2.

%H Michael De Vlieger, <a href="/A156296/b156296.txt">Table of n, a(n) for n = 0..64</a>

%F a(n) = 2*A015502(n+1) for n>1. - _Joe Slater_, Mar 23 2017

%t Table[QPochhammer[-1, 3, n+1]/2^(n+1), {n, 0, 15}] (* _Vaclav Kotesovec_, Mar 24 2017 *)

%K nonn,easy

%O 0,2

%A _Roger L. Bagula_, Feb 07 2009

%E New name from _Joerg Arndt_, Mar 24 2017