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A188387
Central coefficient in (1 + (2^n+1)*x + 2^n*x^2)^n for n>=0.
1
1, 3, 33, 1161, 140545, 63148833, 111254837505, 793938286762113, 23282575640347295745, 2812444483776375381074433, 1393909730376211388561041231873
OFFSET
0,2
LINKS
FORMULA
a(n) = Sum_{k=0..n} C(n,k)^2 * 2^(n*k).
a(n) ~ 2^(n^2). - Vaclav Kotesovec, Feb 12 2015
MATHEMATICA
Table[Sum[Binomial[n, k]^2 * 2^(n*k), {k, 0, n}], {n, 0, 20}] (* Vaclav Kotesovec, Feb 11 2015 *)
PROG
(PARI) {a(n)=polcoeff((1+(2^n+1)*x+2^n*x^2+x*O(x^n))^n, n)}
(PARI) {a(n)=sum(k=0, n, binomial(n, k)^2*2^(n*k))}
(Magma) /*1*/ P<x>:=PolynomialRing(Integers()); [ Coefficients((1+(2^n+1)*x+2^n*x^2)^n)[n+1]: n in [0..10] ]; /*2*/ &cat[ [&+[ Binomial(n, k)^2*2^(n*k): k in [0..n]]]: n in [0..10] ]; // Bruno Berselli, Mar 30 2011
CROSSREFS
Cf. A187021.
Sequence in context: A255883 A215948 A012487 * A113111 A118188 A342170
KEYWORD
nonn
AUTHOR
Paul D. Hanna, Mar 29 2011
STATUS
approved