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Numbers k such that sigma(k)*phi(k) is a palindrome.
2

%I #11 Jul 15 2021 21:23:26

%S 1,2,3,69,219,221,224,254,1772,2181,15463,50807,63551,94236,161257,

%T 602962,2105689,8371756,2115856505,2539027806,5472276593,6819131191,

%U 15442198064,16190055003,46870943027

%N Numbers k such that sigma(k)*phi(k) is a palindrome.

%C a(26) > 5*10^10. 205447718981 is also a term. - _Donovan Johnson_, Sep 30 2011

%e sigma(15463)*phi(15463) = 18056*12972 = 234222432.

%Y Cf. A084122, A115890, A115891.

%K nonn,base

%O 1,2

%A _Giovanni Resta_, Feb 06 2006

%E a(19)-a(25) from _Donovan Johnson_, Sep 30 2011