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A091192 Abundant numbers having at least one abundant proper divisor. 3

%I

%S 24,36,40,48,54,60,72,80,84,90,96,100,108,112,120,126,132,140,144,150,

%T 156,160,162,168,176,180,192,198,200,204,208,210,216,220,224,228,234,

%U 240,252,260,264,270,276,280,288,294,300,306,312,320,324,330,336,340

%N Abundant numbers having at least one abundant proper divisor.

%C A080224(a(n))>1.

%H Amiram Eldar, <a href="/A091192/b091192.txt">Table of n, a(n) for n = 1..10000</a>

%H Eric Weisstein's World of Mathematics, <a href="http://mathworld.wolfram.com/AbundantNumber.html">Abundant Number</a>

%e 24 is in the sequence since it is abundant, and 12 is a divisor of 24 which is also abundant.

%t aQ[n_] := Module[{d = Divisors[n]}, Total@d > 2 n && AnyTrue[d[[2 ;; -2]], DivisorSigma[1, #] > 2# &]]; Select[Range[340], aQ] (* _Amiram Eldar_, Jun 21 2019 *)

%o (PARI) isabund(n) = sigma(n) > 2*n;

%o isok(n) = {if (isabund(n), fordiv(n, d, if ((d<n) && isabund(d), return(1)););); return (0);} \\ _Michel Marcus_, Jun 21 2019

%Y Cf. A005101, A080224, A091191.

%K nonn

%O 1,1

%A _Reinhard Zumkeller_, Dec 27 2003

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Last modified July 5 06:34 EDT 2020. Contains 335459 sequences. (Running on oeis4.)