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

Offset

0,1

Comments

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

a(20) = 287793.

a(21) = 1499553.

a(22) = 11042163.

a(23) = 2832489.

a(24) = 863379.

a(25) = 20160657.

a(26) = 99379467.

a(27) = 5979699.

a(28) = 2590137.

a(30) = 3165723.

a(32) = 3933171.

a(33) = 121463793.

a(35) = 181445913.

a(36) = 9497169.

Links

Table of n, a(n) for n=0..18.

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.

Cf. A200977, A216282, A374294.

Sequence in context: A275792 A010481 A347681 * A291724 A340950 A156550

Adjacent sequences: A374282 A374283 A374284 * A374286 A374287 A374288

Keyword

nonn,more

Author

Seiichi Manyama, Jul 02 2024

Status

approved