A108077 - OEIS

%I #12 Dec 19 2018 19:06:59

%S 2,3,2,5,2,7,2,5,2,11,2,13,2,3,2,17,2,19,2,11,2,23,2,13,2,3,2,29,2,31,

%T 2,17,2,3,2,37,2,3,2,41,2,43,2,23,2,47,2,17,2,11,2,53,2,19,2,29,2,59,

%U 2,61,2,3,2,17,2,67,2,5,2,71,2,73,2,3,2,5,2,79,2,41,2,83,2,43

%N Largest prime p such that p-1 divides n.

%H Antti Karttunen, <a href="/A108077/b108077.txt">Table of n, a(n) for n = 1..16384</a>

%H Antti Karttunen, <a href="/A108077/a108077.txt">Data supplement: n, a(n) computed for n = 1..100000</a>

%p with(numtheory): for n from 1 to 110 do div:=divisors(n): A:=[seq(div[j]+1,j=1..tau(n))]: B:={}: for i from 1 to tau(n) do if isprime(A[i])=true then B:=B union {A[i]} else B:=B: fi: od: C:=convert(B,list): a[n]:=C[nops(C)] od: seq(a[n],n=1..110); # _Emeric Deutsch_, Aug 05 2005

%o (PARI) A108077(n) = fordiv(n,d,if(isprime(1+(n/d)), return(1+(n/d)))); \\ _Antti Karttunen_, Dec 19 2018

%Y Largest term in row n of A108939.

%K nonn,easy

%O 1,1

%A _Philippe Deléham_, Jul 20 2005

%E More terms from _Emeric Deutsch_, Aug 05 2005