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Each term is a sum of two consecutive squares, or a(n) = k^2 + (k+1)^2 for some k. Squares of each term are the hex numbers, or centered hexagonal numbers: a(n) = A001570(n-1) for n>1. - Alexander Adamchuk, Apr 14 2008
Henry MacKean and Victor Moll, Elliptic Curves, Cambridge University Press, New York, 1997, page 22.