OFFSET
1,1
COMMENTS
These numbers are Euler characteristics of Calabi-Yau subvarieties in some weighted projective spaces. See formula B.8 in Bourjaily et alii.
a(n) is divisible by n.
LINKS
Jacob L. Bourjaily, Andrew J. McLeod, Cristian Vergu, Matthias Volk, Matt von Hippel, and Matthias Wilhelm, Embedding Feynman Integral (Calabi-Yau) Geometries in Weighted Projective Space, arXiv:1910.01534 [hep-th], 2019-2020.
FORMULA
a(n) = (1-(1-2*n)^n+2*n^2)/(2*n).
PROG
(Sage) [(1-(1-2*n)**n+2*n**2)/n/2 for n in range(1, 18)]
CROSSREFS
KEYWORD
sign,easy
AUTHOR
F. Chapoton, Dec 10 2022
STATUS
approved