This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A076618 #19 Feb 01 2024 08:30:29
%S A076618 2,3,4,3,6,7,8,3,4,11,12,7,14,15,16,3,18,7,20,11,22,23,24,7,6,27,4,15,
%T A076618 30,31,32,3,34,35,36,7,38,39,40,11,42,43,44,23,16,47,48,7,8,11,52,27,
%U A076618 54,7,56,15,58,59,60,31,62,63,22,3,66,67,68,35,70,71,72,7,74,75,16,39
%N A076618 Least x>1 such that x^d == 1 (mod d) for each divisor d of n.
%H A076618 Amiram Eldar, <a href="/A076618/b076618.txt">Table of n, a(n) for n = 1..10000</a>
%F A076618 If n is prime a(n) = n+1.
%F A076618 For any k a(A000469(k)) = A000469(k)+1.
%F A076618 Sum_{k=1..n} a(k) seems to be asymptotic to c*n^2 with c=0.35... [c = A065463/2 = 0.352221100499... . - _Amiram Eldar_, Feb 01 2024]
%F A076618 a(n) = SquareFreeKernel(n) + 1 = A007947(n) + 1. - _Reinhard Zumkeller_, Aug 10 2004
%t A076618 a[n_] := 1 + Times @@ FactorInteger[n][[;; , 1]]; Array[a, 100] (* _Amiram Eldar_, Feb 01 2024 *)
%o A076618 (PARI) a(n)=if(n<0,0,x=2; while(sumdiv(n,d,(x^d-1)%d)>0,x++); x)
%o A076618 (PARI) a(n) = 1 + vecprod(factor(n)[, 1]); \\ _Amiram Eldar_, Feb 01 2024
%Y A076618 Cf. A000469, A007947, A065463.
%K A076618 nonn
%O A076618 1,1
%A A076618 _Benoit Cloitre_, Oct 22 2002