A111987 Least number having n quadratic residues, or 0 if there is no number.

1, 2, 5, 6, 0, 10, 13, 14, 17, 19, 25, 22, 0, 26, 29, 31, 0, 34, 37, 38, 41, 43, 128, 46, 0, 0, 53, 78, 0, 58, 61, 62, 135, 67, 0, 71, 73, 74, 0, 79, 0, 82, 0, 86, 89, 384, 0, 94, 97, 0, 101, 103, 125, 106, 109, 121, 113, 0, 0, 118, 0, 122, 205, 127, 0, 131, 0, 134, 137, 139, 0

Offset: 1

Author

T. D. Noe, Aug 25 2005

Keywords

• nonn

Examples

			a(4)=6 because, of the five numbers having 4 quadratic residues (6,7,9,12,16), the least is 6.
		

Crossrefs

Cf. A037046 (n such that a(n)=0), A111986 (number of numbers having n quadratic residues), A111988 (greatest number having n quadratic residues).

Programs

Mathematica

t=Table[Length[Union[Mod[Range[0, n/2]^2, n]]], {n, 10000}]; Table[pos=Flatten[Position[t, n]]; If[Length[pos]==0, 0, First[pos]], {n, 100}]