OFFSET
1,2
LINKS
J. Xue, T.-C. Yang, C.-F. Yu, Supersingular abelian surfaces and Eichler class number formula, arXiv preprint arXiv:1404.2978, 2014. See Table 1.
PROG
(Sage)
def a(n):
if n < 4: return [1, 2, 1][n-1]
p = Primes()[n-1]
F = NumberField(x^2 - p, names='a')
hKi = [F.extension(x^2+i+1, names='b').class_number() for i in range(3)]
ans = F.class_number()*F.zeta_function(100)(-1)/2 + hKi[2]/3
if p%4 == 1: ans += hKi[0]/4
else: ans += (3 + 5*(2 - legendre_symbol(2, p)))*hKi[0]/8 + hKi[1]/4
return round(ans.real_part()) # Robin Visser, Feb 23 2024
CROSSREFS
KEYWORD
nonn
AUTHOR
N. J. A. Sloane, Jul 13 2014
EXTENSIONS
More terms from Robin Visser, Feb 23 2024
STATUS
approved