A326008 - OEIS

A326008

G.f.: Sum_{n>=0} (n+1)*(n+2)*(n+3)/3! * x^n * ((1+x)^n + 1)^n / (1 + x*(1+x)^n)^(n+4).

1, 4, 14, 40, 155, 596, 2954, 14784, 83955, 494060, 3112246, 20505484, 141656697, 1020670280, 7650120170, 59509447736, 479350116043, 3990968968884, 34287091686110, 303500118414180, 2764254404207136, 25873492982703592, 248602031383697602, 2449525056696683760, 24727324378709830225, 255512480002690958696, 2700450457984818382502, 29169124796849950540212, 321787888546754475501470, 3623188502069809345093500

(list; graph; refs; listen; history; text; internal format)

OFFSET

0,2

COMMENTS

More generally, the following sums are equal:

(1) Sum_{n>=0} binomial(n+k-1, n) * r^n * (q^n + p)^n / (1 + p*q^n*r)^(n+k),

(2) Sum_{n>=0} binomial(n+k-1, n) * r^n * (q^n - p)^n / (1 - p*q^n*r)^(n+k),

for any fixed integer k; here, k = 4 and q = (1+x), p = 1, r = x. See other examples for k = 1 (A323680), k = 2 (A326006), k = 3 (A326007).

LINKS

Table of n, a(n) for n=0..29.

FORMULA

G.f.: Sum_{n>=0} binomial(n+3,n) * x^n * ((1+x)^n + 1)^n / (1 + x*(1+x)^n)^(n+4).

G.f.: Sum_{n>=0} binomial(n+3,n) * x^n * ((1+x)^n - 1)^n / (1 - x*(1+x)^n)^(n+4).

G.f.: Sum_{n>=0} binomial(n+3,n) * x^n * Sum_{k=0..n} binomial(n,k) * ( (1+x)^n - (1+x)^k )^(n-k).

G.f.: Sum_{n>=0} binomial(n+3,n) * x^n * Sum_{k=0..n} binomial(n,k) * ( (1+x)^n + (1+x)^k )^(n-k) * (-1)^k.

G.f.: Sum_{n>=0} binomial(n+3,n) * x^n * Sum_{k=0..n} binomial(n,k) * Sum_{j=0..n-k} (-1)^j * binomial(n-k,j) * (1 + x)^((n-j)*(n-k)).

FORMULAS INVOLVING TERMS.

a(n) = Sum_{i=0..n} binomial(n-i+3,n-i) * Sum_{j=0..n-i} Sum_{k=0..n-i-j} (-1)^k * binomial(n-i,j) * binomial(n-i-j,k) * binomial((n-i-j)*(n-i-k),i).

a(n) = Sum_{i=0..n} binomial(n-i+3,n-i) * Sum_{j=0..n-i} Sum_{k=0..n-i-j} binomial((n-i-j)*(n-i-k),i) * (-1)^j * (n-i)! / ((n-i-j-k)!*j!*k!).

EXAMPLE

G.f.: A(x) = 1 + 4*x + 14*x^2 + 40*x^3 + 155*x^4 + 596*x^5 + 2954*x^6 + 14784*x^7 + 83955*x^8 + 494060*x^9 + 3112246*x^10 + 20505484*x^11 + 141656697*x^12 + ...

such that

A(x) = 1/(1+x)^4 + 4*x*((1+x) + 1)/(1 + x*(1+x))^5 + 10*x^2*((1+x)^2 + 1)^2/(1 + x*(1+x)^2)^6 + 20*x^3*((1+x)^3 + 1)^3/(1 + x*(1+x)^3)^7 + 35*x^4*((1+x)^4 + 1)^4/(1 + x*(1+x)^4)^8 + 56*x^5*((1+x)^5 + 1)^5/(1 + x*(1+x)^5)^9 + 84*x^6*((1+x)^6 + 1)^6/(1 + x*(1+x)^6)^10 + 120*x^7*((1+x)^7 + 1)^7/(1 + x*(1+x)^7)^11 + ...

also,

A(x) = 1/(1-x)^4 + 4*x*((1+x) - 1)/(1 - x*(1+x))^5 + 10*x^2*((1+x)^2 - 1)^2/(1 - x*(1+x)^2)^6 + 20*x^3*((1+x)^3 - 1)^3/(1 - x*(1+x)^3)^7 + 35*x^4*((1+x)^4 - 1)^4/(1 - x*(1+x)^4)^8 + 56*x^5*((1+x)^5 - 1)^5/(1 - x*(1+x)^5)^9 + 84*x^6*((1+x)^6 - 1)^6/(1 - x*(1+x)^6)^10 + 120*x^7*((1+x)^7 - 1)^7/(1 - x*(1+x)^7)^11 + ...

PROG

(PARI) {a(n) = my(A = sum(m=0, n+1, binomial(m+3, m) * x^m*((1+x +x*O(x^n) )^m - 1)^m/(1 - x*(1+x +x*O(x^n) )^m )^(m+4) )); polcoeff(A, n)}

for(n=0, 35, print1(a(n), ", "))

(PARI) {a(n) = sum(i=0, n, binomial(n-i+3, n-i) * sum(j=0, n-i, sum(k=0, n-i-j, (-1)^k * binomial(n-i, j) * binomial(n-i-j, k) * binomial((n-i-j)*(n-i-k), i) )))}

for(n=0, 35, print1(a(n), ", "))

(PARI) {a(n) = sum(i=0, n, binomial(n-i+3, n-i) * sum(j=0, n-i, sum(k=0, n-i-j, (-1)^j * binomial((n-i-j)*(n-i-k), i) * (n-i)! / ((n-i-j-k)!*j!*k!) )))}

for(n=0, 35, print1(a(n), ", "))

CROSSREFS

Cf. A323680, A326006, A326007.

Sequence in context: A032285 A196451 A196480 * A196713 A375406 A358587

Adjacent sequences: A326005 A326006 A326007 * A326009 A326010 A326011

KEYWORD

nonn

AUTHOR

Paul D. Hanna, Jun 02 2019

STATUS

approved