OFFSET
3,1
COMMENTS
Offset is 3 because a(2) is 3/2, not an integer. - Michel Marcus, Sep 11 2013
LINKS
G. C. Greubel, Table of n, a(n) for n = 3..3000
James East, Ron Niles, Integer polygons of given perimeter, arXiv:1710.11245 [math.CO], 2017.
FORMULA
a(n) = A000031(n)/2.
MATHEMATICA
a[n_] := DivisorSum[n, EulerPhi[#]*2^(n/#)&]/(2n); Table[a[n], {n, 3, 36}] (* Jean-François Alcover, Dec 07 2015 *)
PROG
(PARI) a(n) = sumdiv (n, d, eulerphi(d)*2^(n/d)/(2*n)); \\ Michel Marcus, Sep 11 2013
CROSSREFS
KEYWORD
nonn
AUTHOR
N. J. A. Sloane, Mar 23 2000
STATUS
approved