A026648 Triangular array T read by rows: T(n,0)=T(n,n)=1 for n >= 0; for n >= 2 and 1<=k<=n-1, T(n,k)=T(n-1,k-1)+T(n-2,k-1)+T(n-1,k) if n is even and k is odd, else T(n,k)=t(n-1,k-1)+T(n-1,k).

1, 1, 1, 1, 3, 1, 1, 4, 4, 1, 1, 6, 8, 6, 1, 1, 7, 14, 14, 7, 1, 1, 9, 21, 36, 21, 9, 1, 1, 10, 30, 57, 57, 30, 10, 1, 1, 12, 40, 108, 114, 108, 40, 12, 1, 1, 13, 52, 148, 222, 222, 148, 52, 13, 1, 1, 15, 65, 240, 370, 558, 370, 240, 65, 15, 1, 1, 16

Offset

1,5

Links

Table of n, a(n) for n=1..68.

Formula

T(n, k) = number of paths from (0, 0) to (n-k, k) in the directed graph having vertices (i, j) and edges (i, j)-to-(i+1, j) and (i, j)-to-(i, j+1) for i, j >= 0 and edges (i, j)-to-(i+1, j+1) for i=0, j >= 0 if both i and j are even.

Equals 2*A007318 - A034851 (i.e. twice Pascal's triangle - the Losanitch triangle). - Gary W. Adamson, Dec 31 2007

Crossrefs

Cf. A007318, A034851.

Sequence in context: A238498 A026626 A136482 * A026747 A026374 A174032

Adjacent sequences: A026645 A026646 A026647 * A026649 A026650 A026651

Keyword

nonn,tabl

Author

Clark Kimberling

Status

approved