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A028726
Nonsquares mod 13.
1
2, 5, 6, 7, 8, 11
OFFSET
1,1
EXAMPLE
Since 2 is not a perfect square and there are no solutions to x^2 = 2 mod 13, 2 is in the sequence.
Although 3 is not a perfect square either, there are solutions to x^2 = 3 mod 13, such as x = 4, x = 9. Hence 3 is not in the sequence.
MATHEMATICA
Select[Range[0, 12], JacobiSymbol[#, 13] == -1 &] (* Alonso del Arte, Dec 13 2019 *)
PROG
(Scala) (0 to 12).diff((1 to 13).map(n => (n * n) % 13)) // Alonso del Arte, Dec 13 2019
CROSSREFS
Cf. A010376.
Sequence in context: A028779 A050007 A047579 * A047269 A039027 A129816
KEYWORD
nonn,fini,full
STATUS
approved