Search: id:A063103
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%I A063103
%S A063103 3,8,2667,3937,57337,172011,253921
%N A063103 Numbers n such that sigma(usigma(n) is prime.
%e A063103 n=8: usigma(8) = 9 and sigma(9) = 13, a prime. n=2667: usigma(2667) = 
               4096 and sigma(4096) = 8191, a prime.
%t A063103 us[n_Integer] := (d = Divisors[n]; l = Length[d]; k = 1; s = n; While[k 
               < l, If[ GCD[ d[[k]], n/d[[k]] ] == 1, s = s + d[[k]]]; k++ ]; s); 
               Do[m = n; If[ PrimeQ[ DivisorSigma[1, us[n]]], Print[n]], {n, 1, 
               10^7} ]
%o A063103 (PARI) u(n) = sumdiv(n,d, if(gcd(d, n/d)==1,d)); for(n=1,10^7, if(isprime(sigma(u(n))),
               print(n)))
%Y A063103 Cf. A034448, A063508.
%Y A063103 Sequence in context: A081466 A092592 A162185 this_sequence A058847 A088110 
               A122759
%Y A063103 Adjacent sequences: A063100 A063101 A063102 this_sequence A063104 A063105 
               A063106
%K A063103 nonn
%O A063103 1,1
%A A063103 Jason Earls (zevi_35711(AT)yahoo.com), Aug 07 2001

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