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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
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
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: A037917 A336339 A282146 * A326696 A097603 A374198
KEYWORD
nonn
AUTHOR
Reinhard Zumkeller, Jan 20 2012
STATUS
approved