A184286 Number of distinct n X 3 toroidal 0..4 arrays.

45, 2635, 217125, 20346485, 2034505661, 211927741375, 22706531350485, 2483526875847735, 275947429516276125, 31044085821533856483, 3527737025058633700325, 404219867454740790585125, 46640753937073243032602205, 5413658939124584198288696455

Offset: 1

Author

R. H. Hardin, Jan 10 2011

Keywords

• nonn

Links

• Andrew Howroyd, Table of n, a(n) for n = 1..100

Crossrefs

Column 3 of A184288.

Programs

Mathematica

T[n_, k_] := (1/(n*k))*Sum[Sum[EulerPhi[c]*EulerPhi[d]*5^(n*k/LCM[c, d]), {d, Divisors[k]}], {c, Divisors[n]}]; a[n_] := T[n, 3]; Array[a, 14] (* Jean-François Alcover, Nov 01 2017, after Andrew Howroyd *)

PARI

a(n) = my(k=3); (1/(n*k)) * sumdiv(n, c, sumdiv(k, d, eulerphi(c) * eulerphi(d) * 5^(n*k/lcm(c, d)))); \\ Michel Marcus, Nov 01 2017

Extensions

Terms a(8) and beyond from Andrew Howroyd, Sep 27 2017