A387400 Number of nonnegative s < n such that s^s == s^n (mod n).
1, 1, 1, 2, 1, 4, 2, 3, 3, 5, 1, 7, 2, 6, 8, 7, 3, 8, 2, 9, 7, 5, 2, 12, 5, 6, 9, 11, 2, 15, 3, 15, 8, 7, 9, 13, 2, 8, 8, 17, 5, 18, 3, 11, 14, 7, 2, 24, 9, 13, 10, 14, 1, 20, 11, 17, 9, 8, 1, 27, 4, 9, 19, 31, 15, 18, 3, 12, 10, 22, 2, 23, 5, 9, 17, 13, 16, 23, 4, 33, 26, 10, 1, 31, 13, 9, 12, 20, 4, 27
Offset: 1
Programs
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Magma
[#[s: s in [0..n-1] | Modexp(s,s,n) eq Modexp(s,n,n)]: n in [1..90]];
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PARI
a(n) = sum(s=0, n-1, Mod(s,n)^n == Mod(s, n)^s); \\ Michel Marcus, Aug 30 2025