A115262 Correlation triangle for n+1.
1, 2, 2, 3, 5, 3, 4, 8, 8, 4, 5, 11, 14, 11, 5, 6, 14, 20, 20, 14, 6, 7, 17, 26, 30, 26, 17, 7, 8, 20, 32, 40, 40, 32, 20, 8, 9, 23, 38, 50, 55, 50, 38, 23, 9, 10, 26, 44, 60, 70, 70, 60, 44, 26, 10, 11, 29, 50, 70, 85, 91, 85, 70, 50, 29, 11
Offset: 0
Examples
Triangle begins 1; 2, 2; 3, 5, 3; 4, 8, 8, 4; 5, 11, 14, 11, 5; 6, 14, 20, 20, 14, 6; ... When formatted as a square matrix: 1, 2, 3, 4, 5, ... 2, 5, 8, 11, 14, ... 3, 8, 14, 20, 26, ... 4, 11, 20, 30, 40, ... 5, 14, 26, 40, 55, ... ...
Crossrefs
Programs
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Mathematica
U = NestList[Most[Prepend[#, 0]] &, #, Length[#] - 1] &[Table[k, {k, 1, 12}]]; L = Transpose[U]; M = L.U; TableForm[M] m[i_, j_] := M[[i]][[j]]; Flatten[Table[m[i, n + 1 - i], {n, 1, 12}, {i, 1, n}]] (* Clark Kimberling, Dec 22 2011 *)
Formula
Let f(m,n) = m*(m-1)*(3*n-m-1)/6. This array is (with a different offset) the infinite square array read by antidiagonals U(m,n) = f(n,m) if m < n, U(m,n) = f(m,n) if m <= n. See A271916. - N. J. A. Sloane, Apr 26 2016
G.f.: 1/((1-x)^2*(1-x*y)^2*(1-x^2*y)).
Number triangle T(n, k) = Sum_{j=0..n} [j<=k]*(k-j+1)[j<=n-k]*(n-k-j+1).
T(2n,n) - T(2n,n+1) = n+1.
Comments