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%I A005820 M5376
%S A005820 120,672,523776,459818240,1476304896,51001180160
%N A005820 Triply perfect (tri-perfect, or triperfect) numbers: sum of divisors 
               of n is 3n.
%D A005820 A. Brousseau, Number Theory Tables. Fibonacci Association, San Jose, 
               CA, 1973, p. 138.
%D A005820 J.-M. De Koninck, Ces nombres qui nous fascinent, Entry 120, p. 42, Ellipses, 
               Paris 2008.
%D A005820 R. K. Guy, Unsolved Problems in Number Theory, B2.
%D A005820 N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, 
               Academic Press, 1995 (includes this sequence).
%D A005820 I. Stewart, L'univers des nombres, "Les nombres multiparfaits", Chap.15, 
               pp 82-5, Belin/Pour la Science, Paris 2000.
%D A005820 David Wells, "The Penguin Book of Curious and Interesting Numbers," Penguin 
               Books, London, 1986, pages 135, 159 and 185.
%H A005820 Walter Nissen, <a href="http://upforthecount.com/math/abundance.html">
               Abundancy : Some Resources </a>
%H A005820 Achim Flammenkamp, <a href="http://www.uni-bielefeld.de/~achim/mpn.html">
               The Multiply Perfect Numbers Page</a>
%H A005820 Fred Helenius, <a href="http://pw1.netcom.com/~fredh/index.html">Link 
               to Glossary and Lists</a>
%H A005820 Eric Weisstein's World of Mathematics, <a href="http://mathworld.wolfram.com/
               MultiperfectNumber.html">Link to a section of The World of Mathematics 
               (1).</a>
%H A005820 Eric Weisstein's World of Mathematics, <a href="http://mathworld.wolfram.com/
               Sous-Double.html">Link to a section of The World of Mathematics (2).</
               a>
%e A005820 sigma(120)=360=3*120
%t A005820 AbundantQ[n_]:=DivisorSigma[1, n]==3*n; a={}; Do[If[AbundantQ[n], AppendTo[a, 
               n]], {n, 10^6}]; a [From Vladimir Orlovsky (4vladimir(AT)gmail.com), 
               Aug 07 2008]
%Y A005820 Cf. A007539, A000396, A027687, A046060, A046061.
%Y A005820 Sequence in context: A114887 A069085 A039688 this_sequence A052787 A052769 
               A052766
%Y A005820 Adjacent sequences: A005817 A005818 A005819 this_sequence A005821 A005822 
               A005823
%K A005820 nonn,nice
%O A005820 1,1
%A A005820 N. J. A. Sloane (njas(AT)research.att.com).
%E A005820 Wells gives the 6th term as 31001180160, but this is an error.

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