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Symmetric matrix by antidiagonals: C(max(i+1,j+1),min(i+1,j+1)), i>=1, j>=1.
2

%I #5 Mar 30 2012 18:58:11

%S 1,3,3,6,1,6,10,4,4,10,15,10,1,10,15,21,20,5,5,20,21,28,35,15,1,15,35,

%T 28,36,56,35,6,6,35,56,36,45,84,70,21,1,21,70,84,45,55,120,126,56,7,7,

%U 56,126,120,55,66,165,210,126,28,1,28,126,210,165,66,78,220

%N Symmetric matrix by antidiagonals: C(max(i+1,j+1),min(i+1,j+1)), i>=1, j>=1.

%e Northwest corner:

%e 1....3....6....10...15

%e 3....1....4....10...20

%e 6....4....1....5....15

%e 10...10...5....1....6

%e 15...20...15...6....1

%t g[k_] := k + 1;

%t f[i_, j_] := Binomial[Max[g[i], g[j]], Min[g[i], g[j]]]

%t TableForm[Table[f[i, j], {i, 1, 10}, {j, 1, 10}]]

%t Flatten[Table[f[i, n + 1 - i], {n, 1, 14}, {i, 1, n}]]

%Y Cf. A205456.

%K nonn,tabl

%O 1,2

%A _Clark Kimberling_, Jan 28 2012