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A330404
Least nonsquare k that is a quadratic residue modulo n.
3
2, 2, 3, 5, 5, 3, 2, 8, 7, 5, 3, 12, 3, 2, 6, 17, 2, 7, 5, 5, 7, 3, 2, 12, 6, 3, 7, 8, 5, 6, 2, 17, 3, 2, 11, 13, 3, 5, 3, 20, 2, 7, 6, 5, 10, 2, 2, 33, 2, 6, 13, 12, 6, 7, 5, 8, 6, 5, 3, 21, 3, 2, 7, 17, 10, 3, 6, 8, 3, 11, 2, 28, 2, 3, 6, 5, 11, 3, 2, 20, 7, 2, 3, 21
OFFSET
1,1
COMMENTS
a(n) >= n if and only if n is in A254328.
It seems that lim_{n->oo} a(n)/n = 0. Conjectured last term m such that a(m)/m >= 1/k, k = 1, 2, 3, ...: 16, 48, 240, 288, 720, 720, 720, 720, 1008, 1440, ...
LINKS
EXAMPLE
k is a quadratic residue modulo 16 if and only if k == 0, 1, 4, 9 (mod 16). Since 0, 1, 4, 9 and 16 are squares, a(16) = 17.
k is a quadratic residue modulo 48 if and only if k == 0, 1, 4, 9, 16, 25, 33, 36 (mod 48). Since 0, 1, 4, 9, 16 and 25 are squares, a(48) = 33.
k is a quadratic residue modulo 720 if and only if k == 0, 1, 4, 9, 16, 25, 36, 49, 64, 81, 100, 121, 144, 145, ..., 676 (mod 720). Since 0, 1, 4, ..., 144 are squares, a(720) = 145.
PROG
(PARI) a(n) = my(k=1); while(!issquare(Mod(k, n)) || issquare(k), k++); k
CROSSREFS
A309680 is an alternate version.
Sequence in context: A360461 A284114 A323480 * A340575 A139171 A329570
KEYWORD
nonn
AUTHOR
Jianing Song, Dec 14 2019
STATUS
approved