%I #9 Dec 29 2023 23:23:08
%S 0,0,1,0,4,4,4,0,2,4,4,4,4,8,1,0,4,8,4,4,4,20,4,16,23,12,16,4,4,16,4,
%T 0,25,30,1,20,4,26,22,24,4,22,4,16,19,18,4,16,36,42,1,4,4,46,26,8,28,
%U 6,4,16,4,2,4,0,1,16,4,64,49,36,4,8,4,64,16,44,64,40,4,64,11,64,4,4,16
%N a(n) = 2^sigma(n) mod n.
%H Harvey P. Dale, <a href="/A073816/b073816.txt">Table of n, a(n) for n = 1..1000</a>
%e n=17: sigma(17) = 18, 2^18 = 262144, 262144 mod 17 = 4 = a(17).
%t Table[PowerMod[2,DivisorSigma[1,n],n],{n,90}] (* _Harvey P. Dale_, Jun 23 2014 *)
%Y Cf. A000203, A015910.
%K nonn
%O 1,5
%A _Labos Elemer_, Aug 16 2002