|
| |
|
|
A272715
|
|
Numbers equal to the sum of their proper divisors d such that d mod 3 = 2.
|
|
2
|
| |
|
|
|
OFFSET
|
1,1
|
|
|
COMMENTS
|
The numbers equal to the sum of their proper divisors which are a multiple of 3 are the perfect numbers (A000396) multiplied by 3.
|
|
|
LINKS
|
Table of n, a(n) for n=1..7.
|
|
|
EXAMPLE
|
The proper divisors of 280 which are congruent to 2 mod 3 are 2, 5, 8, 14, 20, 35, 56, and 140. Since their sum is 280, 280 is a term.
|
|
|
MATHEMATICA
|
Select[Range[40000], # == Plus @@ Select[ Most@ Divisors[#], Mod[#, 3] == 2 &] &]
|
|
|
PROG
|
(PARI) is(n)=sumdiv(n, d, if(d%3==2, d, 0))==if(n%3==2, 2*n, n) \\ Charles R Greathouse IV, May 09 2016
|
|
|
CROSSREFS
|
Cf. A272716, A000396, A078182 (sum of proper and improver divisors).
Sequence in context: A094895 A223107 A218411 * A282439 A255498 A091034
Adjacent sequences: A272712 A272713 A272714 * A272716 A272717 A272718
|
|
|
KEYWORD
|
nonn,more
|
|
|
AUTHOR
|
Giovanni Resta, May 05 2016
|
|
|
STATUS
|
approved
|
| |
|
|
