A209411 Number of 2 x 2 matrices M such that M*transpose(M) == 0 mod n.

1, 4, 1, 16, 49, 4, 1, 64, 81, 196, 1, 16, 337, 4, 49, 256, 577, 324, 1, 784, 1, 4, 1, 64, 1825, 1348, 81, 16, 1681, 196, 1, 1024, 1, 2308, 49, 1296, 2737, 4, 337, 3136, 3361, 4, 1, 16, 3969, 4, 1, 256, 2401, 7300, 577, 5392, 5617, 324, 49, 64, 1

Offset

1,2

Links

Joerg Arndt, Table of n, a(n) for n = 1..500

Mathematica

gg[n_] := gg[n] = Flatten[Table[{{x, y}, {z, t}}, {x, n}, {y, n}, {t, n}, {z, n}], 3]; nil[n_] := nil[n] = Length@gg[n][[Select[Range[Length[gg[n]]], Mod[gg[n][[#]].Transpose[gg[n][[#]]], n] == {{0, 0}, {0, 0}} &]]]; Table[Print[nil[n]]; nil[n], {n, 1, 22}]

Crossrefs

Cf. A182039.

Sequence in context: A334063 A111661 A072651 * A369912 A093035 A301624

Adjacent sequences: A209408 A209409 A209410 * A209412 A209413 A209414

Keyword

nonn,mult

Author

José María Grau Ribas, Mar 08 2012

Extensions

Keyword:mult added by Andrew Howroyd, Aug 02 2018

Status

approved