A354597 a(n) is the smallest number k>0 such that -n is not a quadratic residue modulo k.

3, 4, 5, 3, 4, 4, 3, 5, 4, 3, 7, 5, 3, 4, 7, 3, 4, 4, 3, 11, 4, 3, 5, 9, 3, 4, 5, 3, 4, 4, 3, 5, 4, 3, 8, 7, 3, 4, 7, 3, 4, 4, 3, 7, 4, 3, 5, 5, 3, 4, 7, 3, 4, 4, 3, 11, 4, 3, 8, 7, 3, 4, 5, 3, 4, 4, 3, 5, 4, 3, 7, 5, 3, 4, 8, 3, 4, 4, 3, 11, 4, 3, 5, 9, 3, 4, 5, 3, 4, 4, 3, 5, 4, 3, 7, 9, 3, 4, 7, 3

Offset: 1

Author

Bruno Langlois, Jul 08 2022

Keywords

• nonn

Comments

All values are prime powers, and every prime power except 2 appears in the sequence. This can be proved using the Chinese remainder theorem.

Crossrefs

Cf. A139401.

Programs

PARI

a(n) = my(k=2); while (issquare(Mod(-n, k)), k++); k; \\ Michel Marcus, Jul 08 2022