A205545 Symmetric matrix by antidiagonals: C(max(3i,3j),min(3i,3j)), i>=0, j>=0.

1, 1, 1, 1, 1, 1, 1, 20, 20, 1, 1, 84, 1, 84, 1, 1, 220, 84, 84, 220, 1, 1, 455, 924, 1, 924, 455, 1, 1, 816, 5005, 220, 220, 5005, 816, 1, 1, 1330, 18564, 5005, 1, 5005, 18564, 1330, 1, 1, 2024, 54264, 48620, 455, 455, 48620, 54264, 2024, 1, 1, 2925

Offset

1,8

Links

Table of n, a(n) for n=1..57.

Example

Northwest corner:
1.....20....84....220
20....1.....84....924
84....84....1.....220
455...5005..5005..455

Mathematica

f[i_, j_] := Binomial[Max[3 i - 3, 3 j - 3], Min[3 i - 3, 3 j - 3]]
TableForm[Table[f[i, j], {i, 1, 10}, {j, 1, 10}]]
Flatten[Table[f[i, n + 1 - i], {n, 1, 14}, {i, 1, n}]]

Crossrefs

Cf. A205456.

Sequence in context: A261307 A172164 A267058 * A087708 A220022 A217517

Adjacent sequences: A205542 A205543 A205544 * A205546 A205547 A205548

Keyword

nonn,tabl

Author

Clark Kimberling, Jan 28 2012

Status

approved