A187116 - OEIS

%I #6 Mar 30 2012 18:37:26

%S 1,4,20,138,1258,14476,202655,3354848,64246776,1398909332,34157026526,

%T 924757926320,27503093599024,891534666547216,31289986924954924,

%U 1182213869836721036,47846600590876178320,2065282617724684345208

%N A diagonal of triangle A187115.

%C  Definition of triangle: A187115(n,k) = [y^k] R_{n-1}(y+y^2) for k=2..n, n>2, where R_n(y) is the n-th row polynomial with R_2(y)=y^2.

%F Equals column 1 in the matrix square of triangle A135080.

%o (PARI) {a(n)=local(Rn=y^2);for(m=2,n+1,Rn=subst(truncate(Rn),y,y+y^2+O(y^m)));polcoeff(Rn,n,y)}

%Y Cf. A187115, A135082, A187117, A187118, A187119.

%K nonn

%O 2,2

%A _Paul D. Hanna_, Mar 08 2011