A038700 - OEIS

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A038700

Smallest prime == -1 (mod n).

2, 3, 2, 3, 19, 5, 13, 7, 17, 19, 43, 11, 103, 13, 29, 31, 67, 17, 37, 19, 41, 43, 137, 23, 149, 103, 53, 83, 173, 29, 61, 31, 131, 67, 139, 71, 73, 37, 233, 79, 163, 41, 257, 43, 89, 137, 281, 47, 97, 149, 101, 103, 211, 53, 109, 167, 113, 173, 353, 59, 487, 61, 251

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OFFSET

1,1

LINKS

Joerg Arndt, Table of n, a(n) for n = 1..1000

MATHEMATICA

f[n_] := Block[{k = n - 1}, While[ !PrimeQ@k, k += n]; k]; Array[f, 63] (* Robert G. Wilson v, Jun 09 2009 *)

With[{prs=Prime[Range[100]]}, Table[SelectFirst[prs, Mod[#, n]==n-1&], {n, 70}]] (* Harvey P. Dale, Apr 26 2023 *)

PROG

(PARI)

N=10^8; default(primelimit, N);

a(n)=forprime(p=2, 10^7, if(p%n==n-1, return(p)));