# Greetings from The On-Line Encyclopedia of Integer Sequences! http://oeis.org/

Search: id:a241977
Showing 1-1 of 1

%I A241977 #28 Oct 16 2023 04:32:15
%S A241977 3,487,1461,4383,13149,39447,118341,355023,56598313,169794939,
%T A241977 509384817,1754547703,5263643109,7187985751,15790929327,21563957253,
%U A241977 27563378431,33902389487,47372787981,50315900257,64691871759,82690135293,101707168461,150947700771
%N A241977 Numbers k>1 such that 10^phi(k) == 1 (mod k^2), where phi(n)=A000010(n).
%H A241977 Giovanni Resta, <a href="/A241977/b241977.txt">Table of n, a(n) for n = 1..130</a> (terms < 10^15)
%t A241977 Select[Range[400000], PowerMod[10, EulerPhi[#], #^2] == 1 &] (* _Amiram Eldar_, Oct 16 2023 *)
%o A241977 (PARI) for(n=2, 1e9, if(Mod(10, n^2)^(eulerphi(n))==1, print1(n, ", ")))
%Y A241977 Cf. A000010, A045616, A077816, A171928, A242958, A242959, A242960, A245529.
%K A241977 nonn
%O A241977 1,1
%A A241977 _Felix Fröhlich_, Aug 10 2014
%E A241977 Terms a(12) and beyond from _Giovanni Resta_, Jan 24 2020

# Content is available under The OEIS End-User License Agreement: http://oeis.org/LICENSE