A184273 Number of distinct n X 2 toroidal 0..3 arrays.

10, 76, 700, 8296, 104968, 1399176, 19175140, 268447816, 3817763740, 54975738736, 799645010860, 11728126132976, 173215372864600, 2573485530115576, 38430716856090160, 576460752706084936, 8680820741074491040, 131176846752106589576, 1988364834899715824380

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 2 of A184277.

Programs

Mathematica

T[n_, k_] := (1/(n*k))*Sum[Sum[EulerPhi[c]*EulerPhi[d]*4^(n*k/LCM[c, d]), {d, Divisors[k]}], {c, Divisors[n]}]; a[n_] := T[n, 2]; Array[a, 20] (* Jean-François Alcover, Oct 31 2017, after Andrew Howroyd *)

Extensions

Terms a(13) and beyond from Andrew Howroyd, Sep 27 2017