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A251183 a(n) = Sum_{k=0..n} binomial(n,k) * (-1)^(n-k) * (2^k + 1)^k. 2
1, 2, 20, 662, 80744, 38724842, 75185316860, 593940189201662, 19026394370724334544, 2460515237682283759296722, 1280059938187721964276628432100, 2672755638642586172344574379667166822, 22366135140308331991861876017552822964355384, 749476887752252949738787898479359344347670538150842 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,2

LINKS

Table of n, a(n) for n=0..13.

FORMULA

G.f.: Sum_{n>=0} (2^n + 1)^n * x^n / (1+x)^(n+1).

G.f.: Sum_{n>=0} 2^(n^2) * x^n / (1+x - 2^n*x)^(n+1).

a(n) ~ 2^(n^2). - Vaclav Kotesovec, Jan 25 2015

EXAMPLE

G.f.: A(x) = 1 + 2*x + 20*x^2 + 662*x^3 + 80744*x^4 + 38724842*x^5 +...

where we have the identity:

(1) A(x) = 1/(1-x) + (2+1)*x/(1+x)^2 + (2^2+1)^2*x^2/(1+x)^3 + (2^3+1)^3*x^3/(1+x)^4 + (2^4+1)^4*x^4/(1+x)^5 + (2^5+1)^5*x^5/(1+x)^6 +...

(2) A(x) = 1 + 2*x/(1+x - 2*x)^2 + 2^4*x^2/(1+x - 2^2*x)^3 + 2^9*x^3/(1+x - 2^3*x)^4 + 2^16*x^4/(1+x - 2^4*x)^5 + 2^25*x^5/(1+x - 2^5*x)^6 +...

Illustration of initial terms:

a(0) = 1;

a(1) = -1 + (2+1) = 2;

a(2) = 1 - 2*(2+1) + (2^2+1)^2 = 20;

a(3) = -1 + 3*(2+1) - 3*(2^2+1)^2 + (2^3+1)^3 = 662;

a(4) = 1 - 4*(2+1) + 6*(2^2+1)^2 - 4*(2^3+1)^3 + (2^4+1)^4 = 80744;

a(5) = -1 + 5*(2+1) - 10*(2^2+1)^2 + 10*(2^3+1)^3 - 5*(2^4+1)^4 + (2^5+1)^5 = 38724842; ...

MATHEMATICA

Table[Sum[Binomial[n, k] * (-1)^(n-k) * (2^k + 1)^k, {k, 0, n}], {n, 0, 20}] (* Vaclav Kotesovec, Jan 25 2015 *)

PROG

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

for(n=0, 15, print1(a(n), ", "))

(PARI) {a(n)=local(A=1); A=sum(m=0, n, (2^m + 1)^m * x^m / (1+x +x*O(x^n) )^(m+1) ); polcoeff(A, n)}

for(n=0, 15, print1(a(n), ", "))

(PARI) {a(n)=local(A=1); A=sum(m=0, n, 2^(m^2) * x^m / (1+x - 2^m*x +x*O(x^n) )^(m+1) ); polcoeff(A, n)}

for(n=0, 15, print1(a(n), ", "))

CROSSREFS

Cf. A251182, A251184.

Sequence in context: A168480 A198761 A171799 * A158268 A168407 A163594

Adjacent sequences:  A251180 A251181 A251182 * A251184 A251185 A251186

KEYWORD

nonn

AUTHOR

Paul D. Hanna, Jan 19 2015

STATUS

approved

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Last modified July 22 16:43 EDT 2019. Contains 325225 sequences. (Running on oeis4.)