A365326 a(n) is the smallest positive number k such that k^2 - 1 and k^2 + 1 each have exactly n distinct prime divisors.

2, 5, 13, 83, 463, 4217, 169333, 2273237, 23239523, 512974197, 5572561567

Offset: 1

Author

Juri-Stepan Gerasimov, Sep 01 2023

Keywords

• nonn
• more

Crossrefs

Cf. A001221, A180278, A219017.

Cf. A088075 (with k instead of k^2).

Programs

PARI

isok(k, n) = (omega(k^2-1)==n) && (omega(k^2+1)==n);
a(n) = my(k=2); while (!isok(k, n), k++); k; \\ Michel Marcus, Sep 03 2023

Formula

a(n) >= max(A219017(n), A180278(n)). - Daniel Suteu, Sep 03 2023

Extensions

a(9)-a(11) from Amiram Eldar, Sep 03 2023