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A112722 First n-digit number m such that sigma(m) is prime. 0


%S 2,16,289,1681,10201,146689,1190281,10374841,103042801,1023424081,

%T 10009802401,100019755081,1000242014641,10001235475729,

%U 100001580006241,1000017101564209,10000044600049729,100000569832596889

%N First n-digit number m such that sigma(m) is prime.

%C Each term is of the form p^k where p is prime. For n > 1, k is even.

%C Can it be proved that a(n) exists for all n?

%K nonn,base

%O 1,1

%A _Farideh Firoozbakht_, Oct 10 2005

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Last modified September 29 09:23 EDT 2022. Contains 357088 sequences. (Running on oeis4.)