OFFSET
0,3
COMMENTS
"Middle" diagonal of Reinhard Zumkeller's symmetric (Pascal-like) triangular array A100631.
FORMULA
PROG
(PARI) a(n) = {my(m=matrix(n+1, n+1)); for (i=1, n+1, for (j=1, n+1, if ((j==1) || (j==i), m[i, j] = 1, if (j<=n, m[i, j] = 2*(if (i>1, m[i-1, j-1] + m[i-1, j], 0) - if (i>2, m[i-2, j-1], 0) ))); ); ); m[n+1, (n+2)\2]; } \\ Michel Marcus, Feb 10 2021
CROSSREFS
KEYWORD
nonn
AUTHOR
Petros Hadjicostas, Feb 09 2021
STATUS
approved