A390392 Smallest k for which the number of divisors d of k such that d == -d^(k/d) (mod k) is equal to n, or -1 if no such k exists.

1, 2, 30, 390, 6270, 36894, 528990, 6373290, 32222190, 3180844590, 2248482390

Offset

1,2

Links

Table of n, a(n) for n=1..11.

Prog

(Magma) [Min([k: k in [1..5*10^5] | 1 + #[d: d in Divisors(k) | -Modexp(d, k div d, k) mod k eq d] eq n]): n in [1..6]];
(PARI) f(k) = sumdiv(k, d, -Mod(d, k)^(k/d) == d);
list(len) = {my(v = vector(len), c = 0, k = 1, i); while(c < len, i = f(k); if(i <= len && v[i] == 0, c++; v[i] = k); k++); v; } \\ Amiram Eldar, Nov 06 2025

Crossrefs

Cf. A386913.

Sequence in context: A216119 A083446 A392721 * A230726 A091345 A147682

Adjacent sequences: A390389 A390390 A390391 * A390393 A390394 A390395

Keyword

nonn,more

Author

Juri-Stepan Gerasimov, Nov 03 2025

Extensions

a(10)-a(11) from Amiram Eldar, Nov 06 2025

Status

approved