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Modulo 30

Enter an integer to read its residue modulo 30 and determine whether it occupies one of the eight residue classes coprime to 30.

1
7
11
13
17
19
23
29
n mod 30

137 mod 30 = 17

Reduced residue class modulo 30

137 occupies residue class 17, which is coprime to 30.

{ 1, 7, 11, 13, 17, 19, 23, 29 }