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A028732
Nonsquares mod 19.
1
2, 3, 8, 10, 12, 13, 14, 15, 18
OFFSET
1,1
EXAMPLE
Since 10 is not a perfect square, and there are no solutions in integers to x^2 = 10 mod 19, 10 is in the sequence.
Although 11 is not a perfect square either, there are solutions in integers to x^2 = 11 mod 19, such as x = 7, x = 12. Hence 11 is not in the sequence.
MATHEMATICA
Select[Range[18], JacobiSymbol[#, 19] != 1 &] (* Alonso del Arte, Nov 19 2019 *)
PROG
(Scala) val squaresMod19 = (0 to 18).map(n => n * n).map(_ % 19)
(0 to 18).diff(squaresMod19) // Alonso del Arte, Nov 19 2019
CROSSREFS
Sequence in context: A005454 A119187 A008522 * A028751 A325424 A057543
KEYWORD
nonn,fini,full
STATUS
approved