A374285 - OEIS

A374285

a(n) is the smallest nonnegative integer k where there are exactly n nonnegative integer solutions to x^2 + 2*y^2 = k.

5, 0, 9, 81, 297, 891, 1683, 8019, 5049, 18513, 15147, 88209, 31977, 1185921, 136323, 166617, 95931, 7144929, 351747, 4261625379, 287793, 1499553, 11042163, 2832489, 863379, 20160657, 99379467, 5979699, 2590137, 46877879169, 3165723, 2264802453041139, 3933171

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OFFSET

0,1

COMMENTS

For n > 1, a(n) is the smallest nonnegative k such that A216282(k) = n.

LINKS

Seiichi Manyama, Table of n, a(n) for n = 0..100

PROG

(PARI) b(n, k) = sum(i=0, sqrtint(n), sum(j=0, sqrtint(n\k), i^2+k*j^2==n));

a(n, k=2) = my(cnt=0); while(b(cnt, k)!=n, cnt++); cnt;

CROSSREFS

Cf. A374286, A374288.