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A028785 Nonsquares mod 72. 1
2, 3, 5, 6, 7, 8, 10, 11, 12, 13, 14, 15, 17, 18, 19, 20, 21, 22, 23, 24, 26, 27, 29, 30, 31, 32, 33, 34, 35, 37, 38, 39, 41, 42, 43, 44, 45, 46, 47, 48, 50, 51, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 65, 66, 67, 68, 69, 70, 71 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

LINKS

Table of n, a(n) for n=1..60.

EXAMPLE

x^2 = 27 mod 72 has no solutions, so 27 is in the sequence.

x^2 = 28 mod 72 has the following solutions: x = 10, x = 26, x = 46, x = 62. So 28 is not in the sequence.

MATHEMATICA

Complement[Range[71], PowerMod[Range[71], 2, 72]] (* Alonso del Arte, Jan 14 2017 *)

PROG

(Scala) (0 to 71).diff((1 to 72).map(n => (n * n) % 72)) // Alonso del Arte, Dec 24 2019

CROSSREFS

Cf. A010433.

Sequence in context: A028761 A028809 A337533 * A166546 A167759 A028812

Adjacent sequences:  A028782 A028783 A028784 * A028786 A028787 A028788

KEYWORD

nonn,fini,full,easy

AUTHOR

N. J. A. Sloane

STATUS

approved

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Last modified September 21 00:38 EDT 2020. Contains 337265 sequences. (Running on oeis4.)