Search: id:A007620
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%I A007620 M4095
%S A007620 1,6,12,18,20,24,28,30,36,40,42,48,54,56,60,66,72,78,80,84,88,90,96,100,
               104,108,
%T A007620 112,120,126,132,140,144,150,156,160,162,168,176,180,192,196,198,200,204,
               208,
%U A007620 210,216,220,224,228,234,240,252,260,264,270,272,276,280,288,294,300,304,
               306
%N A007620 Practical numbers (second definition): numbers n such that every k <= 
               n is a sum of proper divisors of n (for n>1).
%D A007620 N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, 
               Academic Press, 1995 (includes this sequence).
%D A007620 R. Honsberger, Mathematical Gems, M.A.A., 1973, p. 113.
%D A007620 B. M. Stewart, Sums of distinct divisors, Amer. J. Math., 76 (1954), 
               779-785 quotes Srinivasan [Current Science (1948), p. 179] as using 
               this definition. [R. J. Mathar]
%H A007620 T. D. Noe, <a href="b007620.txt">Table of n, a(n) for n=1..1000</a>
%t A007620 DeleteCases[ A005835, q_/; (Count[ CoefficientList[ Series[ Times@@( 
               (1+z^#)& /@ Divisors[ q ] ), {z, 0, q} ], z ], 0 ]>0) ] - from wouter.meeussen(at)pandora.be
%Y A007620 Cf. A005153 (first definition).
%Y A007620 Sequence in context: A097216 A023196 A005835 this_sequence A100715 A094519 
               A088723
%Y A007620 Adjacent sequences: A007617 A007618 A007619 this_sequence A007621 A007622 
               A007623
%K A007620 nonn,nice,easy
%O A007620 1,2
%A A007620 N. J. A. Sloane (njas(AT)research.att.com), Robert G. Wilson v (rgwv(AT)rgwv.com)

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