login
A188898
The index of the least n-gonal number greater than 1 that is also square, or 0 if none exists.
2
8, 2, 81, 25, 6, 9, 2, 0, 7, 4, 3, 9, 22, 2, 49, 4, 8, 0, 17, 9, 81, 5, 2, 25, 46, 3, 10, 121, 6, 9, 18, 4, 31, 2, 11, 169, 7, 6, 1681, 49, 8, 4, 4961, 12, 225, 8, 2, 16, 32, 0, 49, 25, 17, 13, 289, 9, 49, 7, 27, 81, 118, 2, 136161, 196, 14, 4, 10, 841, 1521
OFFSET
3,1
COMMENTS
Sequence A188896 gives the n that have no solution.
FORMULA
If n is a square, then a(n)=2.
MATHEMATICA
kMax = 25000; NgonIndex[n_, v_] := (-4 + n + Sqrt[16 - 8*n + n^2 - 16*v + 8*n*v])/(n - 2)/2; Table[k = 2; While[sqr = k^2; i = NgonIndex[n, sqr]; k < kMax && ! IntegerQ[i], k++]; If[k == kMax, k = sqr = i = 0]; i, {n, 3, 64}]
CROSSREFS
Cf. A100252 (least square n-gonal number greater than 1).
Sequence in context: A260039 A032761 A262896 * A176860 A281068 A093082
KEYWORD
nonn
AUTHOR
T. D. Noe, Apr 13 2011
STATUS
approved