OFFSET
1,2
LINKS
Andrew Howroyd, Table of n, a(n) for n = 1..100
FORMULA
a(n) = (1/n) * Sum_{d | n} totient(n/d) * A025012(d). - Andrew Howroyd, Mar 02 2017
EXAMPLE
All solutions for n=3:
.-2...-1...-3...-3...-1...-2...-3...-2...-3...-2...-2...-1....0
..1....0....2....1....1....0....0....3....3...-1....2...-1....0
..1....1....1....2....0....2....3...-1....0....3....0....2....0
MATHEMATICA
comps[r_, m_, k_] := Sum[(-1)^i*Binomial[r - 1 - i*m, k - 1]*Binomial[k, i], {i, 0, Floor[(r - k)/m]}]; a[n_Integer, k_] := DivisorSum[n, EulerPhi[n/#] comps[#*(k + 1), 2 k + 1, #] &]/n; a[n_] = a[n, 3]; Array[a, 24] (* Jean-François Alcover, Nov 01 2017, after Andrew Howroyd *)
CROSSREFS
KEYWORD
nonn
AUTHOR
R. H. Hardin, Feb 29 2012
EXTENSIONS
a(20)-a(24) from Andrew Howroyd, Mar 02 2017
STATUS
approved