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A204879 Numbers that can be written as sum of perfect numbers. 4
6, 12, 18, 24, 28, 30, 34, 36, 40, 42, 46, 48, 52, 54, 56, 58, 60, 62, 64, 66, 68, 70, 72, 74, 76, 78, 80, 82, 84, 86, 88, 90, 92, 94, 96, 98, 100, 102, 104, 106, 108, 110, 112, 114, 116, 118, 120, 122, 124, 126, 128, 130, 132, 134, 136, 138, 140, 142, 144 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

Complement of A204878; A097796(a(n)) > 0.

Up to the first odd perfect number (known to be > 10^300, if it exists), also: positive integers of the form 6k+28m, k>=0, m>=0. Contains all even numbers > 50, since any such number is either of the form 6k or 6k+28 or 6k+28*2. - M. F. Hasler, Feb 09 2012

LINKS

Reinhard Zumkeller, Table of n, a(n) for n = 1..1000

Eric Weisstein's World of Mathematics, Perfect Number

Wikipedia, Perfect number

FORMULA

A204879 = { 2k; k>25 } union { 6k; k>0 } union { 28, 34, 40, 46 }

PROG

(Haskell)

import Data.List (findIndices)

a204879 n = a204879_list !! (n-1)

a204879_list = map (+ 1) $ findIndices (> 0) a097796_list

(PARI) (Contribution from M. F. Hasler, Feb 09 2012) (Start)

/* The following code is valid up to occurrence of the first odd perfect number (if it exists), thus at least up to 10^300 */

is_A204879(n)={ n%2&return; n>50 || n%6==0 || n==28 || n==34 || n==40 || n==46 }

A204879(n)={ if(n>12, n+13, 3*n-if(n>4, n*3\2-6))*2 }  \\ (End)

CROSSREFS

Cf. A000396 (perfect numbers).

Sequence in context: A044846 A037917 A282146 * A097603 A315754 A315755

Adjacent sequences:  A204876 A204877 A204878 * A204880 A204881 A204882

KEYWORD

nonn

AUTHOR

Reinhard Zumkeller, Jan 20 2012

STATUS

approved

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Last modified June 15 16:13 EDT 2019. Contains 324142 sequences. (Running on oeis4.)