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%I #3 Mar 30 2012 18:36:58
%S 1,3,18,169,2190,36360,737051,17645187,487025244,15219471545,
%T 530951735025,20447695079658,861389893507518,39394187817328680,
%U 1943446826192453505,102863050524539640435,5813722327999905078450
%N Column 2 of triangle A121420.
%C A121420 is the matrix cube of triangle A121412; row n of triangle T=A121412 equals row (n-1) of T^(n+1) with an appended '1'.
%o (PARI) {a(n)=local(A=Mat(1), B); for(m=1, n+3, B=matrix(m, m); for(i=1, m, for(j=1, i, if(j==i, B[i,j]=1, B[i, j]=(A^i)[i-1, j]); )); A=B); return((A^3)[n+3, 3])}
%Y Cf. A121420 (triangle); other columns: A121421, A121422.
%K nonn
%O 0,2
%A _Paul D. Hanna_, Aug 23 2006
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