OFFSET
0,3
COMMENTS
LINKS
Andrew Howroyd, Table of n, a(n) for n = 0..200
Andrew Howroyd, Chord Configuration Symmetries
FORMULA
MATHEMATICA
a1006[0] = 1; a1006[n_Integer] := a1006[n] = a1006[n-1] + Sum[a1006[k]* a1006[n -2-k], {k, 0, n-2}];
a142150[n_] := n*(1 + (-1)^n)/4;
a2426[n_] := Coefficient[(1 + x + x^2)^n, x, n];
a[0] = 1; a[n_] := (1/n)*(a1006[n]+a142150[n]*a1006[n/2-1] + Sum[EulerPhi[ n/d]*a2426[d], {d, Most @ Divisors[n]}]);
Table[a[n], {n, 0, 40}] (* Jean-François Alcover, Jul 02 2018, after Andrew Howroyd *)
CROSSREFS
KEYWORD
nonn
AUTHOR
Max Alekseyev, Oct 29 2010
STATUS
approved