%I #13 Nov 05 2014 14:18:02
%S 1,3,14,75,439,2718,17483,115575,779716,5342937,37065029,259694334,
%T 1834494025,13048232853,93352065596,671245767795,4847769647701,
%U 35145881098272,255674861620439,1865618971630305,13650358024120804,100123485522075447,736036670999528711
%N G.f.: Sum_{n>=0} x^n / (1-2*x)^(2*n+1) * [Sum_{k=0..n} C(n,k)^2 * x^k] * [Sum_{k=0..n} C(n,k)^2 * 2^k * x^k].
%F G.f.: Sum_{n>=0} x^n * Sum_{k=0..n} C(n,k)^2 * Sum_{j=0..k} C(k,j)^2 * 2^(k-j) * x^j.
%F G.f.: Sum_{n>=0} x^n * Sum_{k=0..n} C(n,k)^2 * 2^(n-k) * Sum_{j=0..k} C(k,j)^2 * x^j.
%F a(n) = Sum_{k=0..[n/2]} Sum_{j=0..n-2*k} C(n-k, k+j)^2 * C(k+j, k)^2 * 2^j.
%F Recurrence: (n-5)*(n-4)*(n-2)*n^2*a(n) = 3*(n-5)*(n-4)*(4*n^3 - 12*n^2 + 10*n - 3)*a(n-1) - (n-5)*(n-4)*(n-1)*(34*n^2 - 102*n + 77)*a(n-2) - 3*(n-5)*(n-2)*(2*n-5)*a(n-3) + (n-3)*(53*n^4 - 636*n^3 + 2617*n^2 - 4254*n + 2226)*a(n-4) - 3*(n-4)*(n-1)*(2*n-7)*a(n-5) - (n-5)*(n-2)*(n-1)*(34*n^2 - 306*n + 689)*a(n-6) + 3*(n-2)*(n-1)*(4*n^3 - 60*n^2 + 298*n - 489)*a(n-7) - (n-6)^2*(n-4)*(n-2)*(n-1)*a(n-8). - _Vaclav Kotesovec_, Aug 27 2014
%F a(n) ~ c * d^n / n, where d = 5/2 + sqrt(2) + sqrt(29+20*sqrt(2))/2 = 7.698532234454699125... is the root of the equation d^4 - 10*d^3 + 19*d^2 - 10*d + 1 = 0, and c = 0.51515814369432019442929480754730417101213524575391074352368... . - _Vaclav Kotesovec_, Aug 27 2014
%e G.f.: A(x) = 1 + 3*x + 14*x^2 + 75*x^3 + 439*x^4 + 2718*x^5 + 17483*x^6 +...
%e where the g.f. is given by the binomial series:
%e A(x) = 1/(1-2*x) + x/(1-2*x)^3 * (1+x) * (1+2*x)
%e + x^2/(1-2*x)^5 * (1 + 2^2*x + x^2) * (1 + 2^2*2*x + 4*x^2)
%e + x^3/(1-2*x)^7 * (1 + 3^2*x + 3^2*x^2 + x^3) * (1 + 3^2*2*x + 3^2*4*x^2 + 8*x^3)
%e + x^4/(1-2*x)^9 * (1 + 4^2*x + 6^2*x^2 + 4^2*x^3 + x^4) * (1 + 4^2*2*x + 6^2*4*x^2 + 4^2*8*x^3 + 16*x^4)
%e + x^5/(1-2*x)^11 * (1 + 5^2*x + 10^2*x^2 + 10^2*x^3 + 5^2*x^4 + x^5) * (1 + 5^2*2*x + 10^2*4*x^2 + 10^2*8*x^3 + 5^2*16*x^4 + 32*x^5) +...
%e We can also express the g.f. by the binomial series:
%e A(x) = 1 + x*(1 + (2+x)) + x^2*(1 + 2^2*(2+x) + (4+2^2*2*x+x^2))
%e + x^3*(1 + 3^2*(2+x) + 3^2*(4+2^2*2*x+x^2) + (8+3^2*4*x+3^2*2*x^2+x^3))
%e + x^4*(1 + 4^2*(2+x) + 6^2*(4+2^2*2*x+x^2) + 4^2*(8+3^2*4*x+3^2*2*x^2+x^3) + (16+4^2*8*x+6^2*4*x^2+4^2*2*x^3+x^4))
%e + x^5*(1 + 5^2*(2+x) + 10^2*(4+2^2*2*x+x^2) + 10^2*(8+3^2*4*x+3^2*2*x^2+x^3) + 5^2*(16+4^2*8*x+6^2*4*x^2+4^2*2*x^3+x^4) + (32+5^2*16*x+10^2*8*x^2+10^2*4*x^3+5^2*2*x^4+x^5)) +...
%t Table[Sum[Sum[Binomial[n-k, k+j]^2 * Binomial[k+j, k]^2 * 2^j,{j,0,n-2*k}],{k,0,Floor[n/2]}],{n,0,20}] (* _Vaclav Kotesovec_, Aug 27 2014 *)
%o (PARI) /* By definition: */
%o {a(n)=local(A=1); A=sum(m=0, n, x^m/(1-2*x)^(2*m+1) * sum(k=0, m, binomial(m, k)^2*x^k) * sum(k=0, m, binomial(m, k)^2*2^k*x^k) +x*O(x^n)); polcoeff(A, n)}
%o for(n=0, 30, print1(a(n), ", "))
%o (PARI) /* By a binomial identity: */
%o {a(n)=polcoeff(sum(m=0, n, x^m*sum(k=0, m, binomial(m, k)^2*sum(j=0, k, binomial(k, j)^2*2^(k-j)*x^j)+x*O(x^n))), n)}
%o for(n=0, 30, print1(a(n), ", "))
%o (PARI) /* By a binomial identity: */
%o {a(n)=polcoeff(sum(m=0, n, x^m*sum(k=0, m, binomial(m, k)^2 * 2^(m-k) * sum(j=0, k, binomial(k, j)^2*x^j)+x*O(x^n))), n)}
%o for(n=0, 30, print1(a(n), ", "))
%o (PARI) /* Formula for a(n): */
%o {a(n)=sum(k=0, n\2, sum(j=0, n-2*k, binomial(n-k, k+j)^2*binomial(k+j, k)^2*2^j))}
%o for(n=0, 30, print1(a(n), ", "))
%Y Cf. A243948 (dual), A246538.
%K nonn
%O 0,2
%A _Paul D. Hanna_, Aug 26 2014
%E Minor edits by _Vaclav Kotesovec_, Nov 05 2014