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 A028726 Nonsquares mod 13. 1
 2, 5, 6, 7, 8, 11 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 LINKS 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 Adjacent sequences:  A028723 A028724 A028725 * A028727 A028728 A028729 KEYWORD nonn,fini,full AUTHOR STATUS approved

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Last modified May 28 17:37 EDT 2020. Contains 334684 sequences. (Running on oeis4.)