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A028743 Nonsquares mod 30. 1
2, 3, 5, 7, 8, 11, 12, 13, 14, 17, 18, 20, 22, 23, 26, 27, 28, 29 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

LINKS

Table of n, a(n) for n=1..18.

EXAMPLE

Since 5 is not a perfect square and there are no solutions to x^2 = 5 mod 30, 5 is in the sequence.

Although 6 is not a perfect square either, there are solutions to x^2 = 6 mod 30, such as x = 6, x = 24, so 6 is not in the sequence.

MATHEMATICA

Complement[Range[30], PowerMod[Range[30], 2, 30]] (* Alonso del Arte, Nov 30 2019 *)

PROG

(Scala) val squaresMod30 = (1 to 30).map(n => n * n).map(_ % 30)

(0 to 29).diff(squaresMod30) // Alonso del Arte, Nov 30 2019

CROSSREFS

Cf. A010462.

Sequence in context: A028728 A286758 A106735 * A082634 A100959 A245303

Adjacent sequences:  A028740 A028741 A028742 * A028744 A028745 A028746

KEYWORD

nonn,fini,full,changed

AUTHOR

N. J. A. Sloane

EXTENSIONS

Incorrect term 15 removed by Alonso del Arte, Nov 30 2019

STATUS

approved

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Last modified December 13 17:09 EST 2019. Contains 329970 sequences. (Running on oeis4.)