OFFSET
1,2
REFERENCES
V. A. Liskovets and A. Mednykh, Enumeration of subgroups in the fundamental groups of orientable circle bundles over surfaces, Commun. in Algebra, 28, No. 4 (2000), 1717-1738.
R. P. Stanley, Enumerative Combinatorics, Cambridge, Vol. 2, 1999; see Problem 5.13(c), Eq. (5.125).
FORMULA
a(n) = Sum_{m|n} A003319(m+1) * (n/m)^(m+1). - Sean A. Irvine, Dec 06 2019
CROSSREFS
KEYWORD
nonn
AUTHOR
EXTENSIONS
More terms from Sean A. Irvine, Dec 06 2019
STATUS
approved