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A374288
a(n) is the smallest nonnegative integer k where there are exactly n nonnegative integer solutions to x^2 + 5*y^2 = k.
2
2, 0, 9, 81, 189, 441, 1449, 10206, 3969, 12789, 13041, 35721, 30429, 194481, 117369, 115101, 186921, 2893401, 273861
OFFSET
0,1
COMMENTS
For n > 1, a(n) is the smallest nonnegative k such that A216283(k) = n.
a(20) = 378189.
a(21) = 1035909.
a(22) = 9506889.
a(23) = 2099601.
a(24) = 882441.
a(25) = 5639949.
a(26) = 85562001.
a(27) = 6765381.
a(28) = 3403701.
a(30) = 3925341.
a(32) = 5420709.
a(33) = 83908629.
a(35) = 50759541.
a(36) = 7941969.
a(38) = 102880449.
a(40) = 15505749.
a(41) = 170067681.
a(42) = 35328069.
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=5) = my(cnt=0); while(b(cnt, k)!=n, cnt++); cnt;
CROSSREFS
Cf. A216283.
Sequence in context: A299626 A002741 A213322 * A368703 A345048 A151887
KEYWORD
nonn,more
AUTHOR
Seiichi Manyama, Jul 02 2024
STATUS
approved