OFFSET
0,2
PROG
(PARI) a(n)=local(A, B); A=Mat(1); for(m=2, n+1, B=matrix(m, m); for(i=1, m, for(j=1, i, if(i<3 || j==i || j>m-1, B[i, j]=1, if(j==1, B[i, 1]=1, B[i, j]=(A^(3*j-2))[i-j+1, 1])); )); A=B); (matrix(#A, #A, r, c, if(r>=c, (A^(3*c))[r-c+1, 1]))^3)[n+1, 1]
CROSSREFS
KEYWORD
nonn
AUTHOR
Paul D. Hanna, Nov 14 2005
STATUS
approved