A374161 - OEIS

A374161

a(n) is the smallest nonnegative integer k where exactly n pairs of positive integers (x, y) exist such that x^2 + 19*y^2 = k.

0, 20, 140, 700, 1540, 17500, 7700, 122500, 26180, 53900, 192500, 7035875, 130900, 592900, 4812500, 1347500, 602140, 150062500, 916300, 879484375, 3272500, 33687500, 14822500, 7015421875, 3010700, 66027500, 809125625, 10079300, 81812500, 549266265625, 22907500

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OFFSET

0,2

LINKS

Martin Fuller, Table of n, a(n) for n = 0..57

PROG

(Python)

from itertools import count

from sympy.abc import x, y

from sympy.solvers.diophantine.diophantine import diop_quadratic

def A374161(n): return next(m for m in count(0) if sum(1 for d in diop_quadratic(x**2+19*y**2-m) if d[0]>0 and d[1]>0)==n) # Chai Wah Wu, Jun 30 2024

CROSSREFS