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A198471 Abundant numbers that are smaller than the sum of their deficient divisors. 3

%I

%S 20,30,42,66,70,78,88,102,104,114,138,150,174,186,210,220,222,246,258,

%T 260,272,282,294,304,308,318,330,340,354,364,366,368,380,390,402,426,

%U 438,450,460,462,464,474,476,498,510,532,534,546,550,570,572,580,582,606

%N Abundant numbers that are smaller than the sum of their deficient divisors.

%C The primitive abundant number sequence (A071395) is a subset of this sequence.

%H Amiram Eldar, <a href="/A198471/b198471.txt">Table of n, a(n) for n = 1..10000</a>

%e a(5) = 70 since 70 is smaller than 74, which is the sum of its deficient divisors.

%t totdef[n_] := Total@Select[Divisors@n, DivisorSigma[-1, #] < 2 &]; Select[Range[570], DivisorSigma[-1, #] > 2 && # < totdef[#] &] (* _Giovanni Resta_, Jan 09 2013 *)

%o (PARI) isok(n) = (sigma(n) > 2*n) && (n < sumdiv(n, d, if (sigma(d) < 2*d, d))); \\ _Michel Marcus_, Jun 21 2019

%Y Cf. A071395, A198471, A125310.

%K nonn

%O 1,1

%A _Timothy L. Tiffin_, Jan 07 2013

%E a(21)-a(50) from _Giovanni Resta_, Jan 09 2013

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Last modified January 25 01:37 EST 2020. Contains 331229 sequences. (Running on oeis4.)