OFFSET
1,1
LINKS
Michael De Vlieger, Table of n, a(n) for n = 1..3320
Dennis S. Bernstein, Omran Kouba, Counting Colorful Necklaces and Bracelets in Three Colors, arXiv:1901.10703 [math.CO], 2019.
MAPLE
See A306888.
MATHEMATICA
Table[DivisorSum[n, (2^# - (-1)^#) EulerPhi[3 n/#] &], {n, 10^4}] (* Michael De Vlieger, Mar 18 2019 *)
PROG
(PARI) a(n) = sumdiv(n, d, (2^d - (-1)^d)*eulerphi(3*n/d)); \\ Michel Marcus, Mar 16 2019
CROSSREFS
KEYWORD
nonn
AUTHOR
Michael De Vlieger and N. J. A. Sloane, Mar 15 2019
STATUS
approved