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A125640 Primitive doubly abundant numbers - doubly abundant numbers that are not the multiple of another doubly abundant number. 2
24, 30, 42, 54, 66, 78, 102, 114, 138, 140, 174, 176, 186, 222, 224, 246, 258, 282, 308, 318, 340, 354, 364, 366, 380, 402, 426, 438, 440, 474, 476, 498, 520, 532, 534, 580, 582, 606, 618, 642, 644, 654, 678, 762, 786, 812, 822, 834, 868, 894 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

Are there infinitely many primitive doubly abundant numbers?

LINKS

Reinhard Zumkeller, Table of n, a(n) for n = 1..10000

EXAMPLE

42 is a primitive doubly abundant number because it is abundant (s(42) = 54), the sum of its proper divisors is abundant (s(54) = 66) and no divisor of 42 is doubly abundant.

PROG

(Haskell)

import Data.List (intersect)

a125640 n = a125640_list !! (n-1)

a125640_list = f a125639_list [] where

   f (x:xs) ys = if null (a027751_row' x `intersect` ys)

                    then x : f xs (x : ys) else f xs ys

-- Reinhard Zumkeller, Oct 31 2015

CROSSREFS

Cf. A005101, A125639.

Cf. A027751.

Sequence in context: A335054 A125639 A076496 * A141545 A106682 A334790

Adjacent sequences:  A125637 A125638 A125639 * A125641 A125642 A125643

KEYWORD

nonn

AUTHOR

Gabriel Cunningham (gabriel.cunningham(AT)gmail.com), Nov 28 2006

EXTENSIONS

Data corrected by Reinhard Zumkeller, Oct 31 2015

STATUS

approved

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Last modified April 10 08:09 EDT 2021. Contains 342845 sequences. (Running on oeis4.)