%I A123091
%S A123091 1,2,3,4,5,7,10,11,13,15,17,19,20,23,29,31,37,41,43,47,53,59,61,65,67,
%T A123091 71,73,79,83,89,97,101,103,107,109,113,124,127,131,137,139,149,151,157,
%U A123091 163,167,173,179,181,190,191,193,197,199,211,217,223,227,229,233,239
%N A123091 Numbers n such that n divides 5^n - 5.
%C A123091 All primes are the terms of a(n). Nonprimes in a(n) are listed in A122782(n) 
               = {1,4,10,15,20,65,124,190,217,310,435,561,781,...}. All pseudoprimes 
               to base 5 are the terms of a(n). They are listed in A005936(n) = 
               {4,124,217,561,781,...}. Numbers n up to 10^6 such that n divides 
               5^n + 5 are {1,2,5,6,10,30,70,1565,2806,3126,51670,58290,214405,285286,
               378258}.
%t A123091 Select[Range[1000], IntegerQ[(PowerMod[5,#,# ]-5)/# ]&]
%Y A123091 Cf. A122782 - Nonprimes n such that 5^n==5 (mod n). Cf. A005936 - Pseudoprimes 
               to base 5. Cf. A067946 - Numbers n such that n divides 5^n-1. Cf. 
               A015951 - Numbers n such that n | 5^n + 1.
%Y A123091 Sequence in context: A117092 A002504 A133431 this_sequence A160512 A144430 
               A157082
%Y A123091 Adjacent sequences: A123088 A123089 A123090 this_sequence A123092 A123093 
               A123094
%K A123091 nonn
%O A123091 1,2
%A A123091 Alexander Adamchuk (alex(AT)kolmogorov.com), Nov 04 2006