OFFSET
1,1
LINKS
Andrew Howroyd, Table of n, a(n) for n = 1..25
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, n]; Array[a, 10] (* Jean-François Alcover, Oct 31 2017, after Andrew Howroyd *)
CROSSREFS
KEYWORD
nonn
AUTHOR
R. H. Hardin, Jan 10 2011
EXTENSIONS
Terms a(6) and beyond from Andrew Howroyd, Sep 27 2017
STATUS
approved