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A206158 a(n) = Sum_{k=0..n} binomial(n,k)^(2*k+1). 4
1, 2, 10, 272, 24226, 12053252, 40086916024, 429254371605824, 23527609330364490754, 10714627376371224032350052, 16964729291782419425708732425300, 109783535843179466164398767001178968704, 6782057095273243388704415924996348722446049600 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,2

COMMENTS

Ignoring initial term a(0), equals the logarithmic derivative of A206157.

LINKS

Table of n, a(n) for n=0..12.

FORMULA

Limit n->infinity a(n)^(1/n^2) = r^(2*r^2/(1-2*r)) = 2.3520150420944489879258119..., where r = 0.70350607643066243... (see A220359) is the root of the equation (1-r)^(2*r-1) = r^(2*r). - Vaclav Kotesovec, Mar 03 2014

EXAMPLE

L.g.f.: L(x) = 2*x + 10*x^2/2 + 272*x^3/3 + 24226*x^4/4 + 12053252*x^5/5 +...

where exponentiation yields A206157:

exp(L(x)) = 1 + 2*x + 7*x^2 + 102*x^3 + 6261*x^4 + 2423430*x^5 + 6686021554*x^6 +...

Illustration of initial terms:

a(1) = 1^1 + 1^3 = 2;

a(2) = 1^1 + 2^3 + 1^5 = 10;

a(3) = 1^1 + 3^3 + 3^5 + 1^7 = 272;

a(4) = 1^1 + 4^3 + 6^5 + 4^7 + 1^9 = 24226;

a(5) = 1^1 + 5^3 + 10^5 + 10^7 + 5^9 + 1^11 = 12053252; ...

MATHEMATICA

Table[Sum[Binomial[n, k]^(2*k+1), {k, 0, n}], {n, 0, 20}] (* Vaclav Kotesovec, Mar 03 2014 *)

PROG

(PARI) {a(n)=sum(k=0, n, binomial(n, k)^(2*k+1))}

for(n=0, 16, print1(a(n), ", "))

CROSSREFS

Cf. A206157 (exp), A184731, A206154, A206156, A206152, A220359.

Sequence in context: A134473 A005154 A074056 * A144288 A215286 A260231

Adjacent sequences:  A206155 A206156 A206157 * A206159 A206160 A206161

KEYWORD

nonn

AUTHOR

Paul D. Hanna, Feb 04 2012

STATUS

approved

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Last modified September 17 06:52 EDT 2019. Contains 327119 sequences. (Running on oeis4.)