cp's OEIS Frontend

A270838 Largest value k < p-2 such that k! mod p = 1 with p = prime(n).

%I A270838 #8 Mar 01 2020 16:44:45
%S A270838 1,1,1,1,11,1,11,10,15,1,1,1,1,37,29,52,48,35,55,1,46,67,53,1,96,53,
%T A270838 22,1,1,1,120,122,123,75,1,1,83,1,1,1,1,90,1,117,105,111,82,1,168,119,
%U A270838 1,125,1,1,1,135,236,1,141,1,153,281,1,1,231,1,1,1,1,236
%N A270838 Largest value k < p-2 such that k! mod p = 1 with p = prime(n).
%H A270838 Alois P. Heinz, <a href="/A270838/b270838.txt">Table of n, a(n) for n = 3..4555</a>
%p A270838 a:= proc(n) option remember; local k, p; p:=ithprime(n);
%p A270838       for k from p-3 by -1 do if irem(k!, p)=1 then return k fi od
%p A270838     end:
%p A270838 seq(a(n), n=3..100);
%t A270838 lvk[n_]:=Module[{p=Prime[n],k},k=p-3;While[Mod[k!,p]!=1,k--];k]; Array[ lvk,80,3] (* _Harvey P. Dale_, Mar 01 2020 *)
%Y A270838 Cf. A000040, A270780.
%K A270838 nonn
%O A270838 3,5
%A A270838 _Alois P. Heinz_, Mar 23 2016