OFFSET
1,2
COMMENTS
Numbers k such that k divides A130072(k) are listed in A130073(n) = {1,2,3,4,5,6,7,8,9,11,12,13,15,16,17,18,19,23,24,25,27,29,31,32,36,37,41,43,...}, which includes all primes. a(n) includes nonprimes in A130073(n). p^(k+1) divides A130072(p^k) for prime p = {2,3,5,19} = A130076(n) and all k>0. It appears that a(n) includes all powers p^k of primes p = {2,3,5,19} for k>1 and all powers of numbers of the form 2^k*3^m, 3^k*5^m, 5^k*19^m.
LINKS
Amiram Eldar, Table of n, a(n) for n = 1..10000
MATHEMATICA
Select[Range[10000], !PrimeQ[ # ]&&IntegerQ[(PowerMod[5, #, # ]-PowerMod[3, #, # ]-PowerMod[2, #, # ])/# ]&]
CROSSREFS
KEYWORD
nonn
AUTHOR
Alexander Adamchuk, May 06 2007
STATUS
approved