A188893 The index of the least triangular number greater than 1 that is also an n-gonal number, or 0 if none exists.

2, 8, 20, 3, 10, 6, 25, 4, 0, 14, 8, 50, 5, 9, 21, 0, 43, 23, 6, 154, 11, 16, 26, 56, 12, 7, 49, 34, 40, 342, 19, 25, 1634, 8, 115, 0, 33, 89, 15, 47, 54, 638, 9, 36, 117, 30, 99, 204, 38, 17, 146, 133, 10, 62, 70, 18, 41, 49, 34, 4806, 105, 161, 329, 11, 439, 223, 28, 5974, 20, 79

Offset

3,1

Links

Table of n, a(n) for n=3..72.

Mathematica

NgonIndex[n_, v_] := (-4 + n + Sqrt[16 - 8*n + n^2 - 16*v + 8*n*v])/(n - 2)/2; Table[k = 2; While[tr = k*(k+1)/2; i = NgonIndex[n, tr]; k < 20000 && ! IntegerQ[i], k++]; If[k==20000, k=0]; k, {n, 3, 50}]

Crossrefs

Cf. A188891.

Sequence in context: A240285 A129445 A082821 * A227127 A227399 A327098

Adjacent sequences: A188890 A188891 A188892 * A188894 A188895 A188896

Keyword

nonn

Author

T. D. Noe, Apr 13 2011

Status

approved