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%I #15 Dec 12 2022 18:17:04
%S 2,0,24,-296,5910,-147624,4482044,-160180656,6588215370,-306553312880,
%T 15921704570112,-913109351334168,57312158437875614,
%U -3907821040411155672,287639624919939481380,-22731972554599539494624,1919809166125424793288978,-172552913868209944831000416
%N Euler characteristics of some Calabi-Yau n-folds.
%C These numbers are Euler characteristics of Calabi-Yau subvarieties in some weighted projective spaces. See formula B.8 in Bourjaily et alii.
%C a(n) is divisible by n.
%H Jacob L. Bourjaily, Andrew J. McLeod, Cristian Vergu, Matthias Volk, Matt von Hippel, and Matthias Wilhelm, <a href="https://arxiv.org/abs/1910.01534">Embedding Feynman Integral (Calabi-Yau) Geometries in Weighted Projective Space</a>, arXiv:1910.01534 [hep-th], 2019-2020.
%F a(n) = (1-(1-2*n)^n+2*n^2)/(2*n).
%o (Sage) [(1-(1-2*n)**n+2*n**2)/n/2 for n in range(1,18)]
%K sign,easy
%O 1,1
%A _F. Chapoton_, Dec 10 2022