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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

Table of n, a(n) for n=1..6.

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

N. J. A. Sloane

STATUS

approved

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