A098730 - OEIS

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A098730

Sum[i=0..n, Sum[j=0..n, C(n-i,i+j) * C(n-j,i+j) ]].

%I #4 Jan 25 2023 19:58:05

%S 1,1,5,14,46,145,462,1465,4641,14671,46298,145858,458811,1441204,

%T 4521255,14167145,44344445,138665650,433218100,1352333899,4218220602,

%U 13148256139,40956562683,127501720725,396702130246,1233632920766

%N Sum[i=0..n, Sum[j=0..n, C(n-i,i+j) * C(n-j,i+j) ]].

%t Table[Sum[Sum[Binomial[n-i,i+j]Binomial[n-j,i+j],{j,0,n}],{i,0,n}],{n,0,30}] (* _Harvey P. Dale_, Jan 25 2023 *)

%K nonn

%O 0,3

%A _Ralf Stephan_, Oct 28 2004