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A198471 Abundant numbers that are smaller than the sum of their deficient divisors. 3
20, 30, 42, 66, 70, 78, 88, 102, 104, 114, 138, 150, 174, 186, 210, 220, 222, 246, 258, 260, 272, 282, 294, 304, 308, 318, 330, 340, 354, 364, 366, 368, 380, 390, 402, 426, 438, 450, 460, 462, 464, 474, 476, 498, 510, 532, 534, 546, 550, 570, 572, 580, 582, 606 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

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

LINKS

Amiram Eldar, Table of n, a(n) for n = 1..10000

EXAMPLE

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

MATHEMATICA

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

PROG

(PARI) isok(n) = (sigma(n) > 2*n) && (n < sumdiv(n, d, if (sigma(d) < 2*d, d))); \\ Michel Marcus, Jun 21 2019

CROSSREFS

Cf. A071395, A198471, A125310.

Sequence in context: A109944 A108030 A095787 * A120145 A104048 A078499

Adjacent sequences:  A198468 A198469 A198470 * A198472 A198473 A198474

KEYWORD

nonn

AUTHOR

Timothy L. Tiffin, Jan 07 2013

EXTENSIONS

a(21)-a(50) from Giovanni Resta, Jan 09 2013

STATUS

approved

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Last modified December 8 04:31 EST 2019. Contains 329850 sequences. (Running on oeis4.)