A385074 Index of the first occurrence of n in A385073.

1, 2, 20737, 4, 9, 6, 3763, 20, 40369, 35, 2951, 16, 35622023, 27, 2041, 49, 25, 42, 697, 2168, 18537061, 31958, 117, 66, 356698651, 147, 7863277, 28

Offset: 0

Author

Robert G. Wilson v, Jun 16 2025

Keywords

• nonn
• more

Comments

a(28) if it exists exceeds 10^11.

Although the parity of n and a(n) are often the opposite, it is not a requirement. Cases in point, n = {9, 13, 15, 25}.

Crossrefs

Cf. A385073.

Programs

Mathematica

f[n_] := Block[{b = 2}, While[GCD[n, b] > 1, b++]; PowerMod[b, n - 1, n]]; k = 1; t[_] := 0; While[ k < 10^10, a = f@k; If[ a < 1001 && t[a] == 0, t[a] = k]; k++]; t /@ Range[0, 27]

PARI

f(n) = forprime(p=2, , if(n%p, return(lift(Mod(p, n)^(n-1))))); \\ A385073
a(n) = my(k=1); while (f(k) != n, k++); k; \\ Michel Marcus, Jun 18 2025