A092473 a(n) = Sum_{i+j+k=n, 0<=i<=j<=k<=n} (2n)!/((i+j)! * (j+k)! * (k+i)!).

1, 2, 18, 170, 1330, 11382, 117810, 934362, 8611746, 82240730, 699393838, 6244164940, 59910383026, 507902083210, 4599466921410, 43063170064620, 372282144948450, 3338235118237410, 31231394376541650, 270058012725600000

Offset: 0

Author

Benoit Cloitre, Mar 25 2004

Keywords

• nonn

Links

• Vaclav Kotesovec, Table of n, a(n) for n = 0..1000 (terms 0..200 from Seiichi Manyama)
• Vaclav Kotesovec, Plot a(n+1)/a(n) for n = 1..999

Crossrefs

Cf. A092472.

Programs

PARI

a(n)=sum(i=0,n,sum(j=0,i,sum(k=0,j,if(i+j+k-n,0,(2*n)!/(i+j)!/(j+k)!/(k+i)!))))