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

1,1

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.

Links

Table of n, a(n) for n=1..100.

Prog

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

Crossrefs

Cf. A139401.

Sequence in context: A163874 A165565 A033706 * A121890 A330740 A178231

Adjacent sequences: A354594 A354595 A354596 * A354598 A354599 A354600

Keyword

nonn

Author

Bruno Langlois, Jul 08 2022

Status

approved