|
|
A245774
|
|
Numbers k that divide 3*sigma(k).
|
|
3
|
|
|
1, 3, 6, 12, 28, 84, 120, 234, 270, 496, 672, 1080, 1488, 1638, 6048, 6552, 8128, 24384, 30240, 32760, 35640, 199584, 435708, 523776, 2142720, 2178540, 4713984, 12999168, 18506880, 23569920, 33550336, 36197280, 45532800
(list;
graph;
refs;
listen;
history;
text;
internal format)
|
|
|
OFFSET
|
1,2
|
|
COMMENTS
|
Numbers k that divide 3*A000203(k).
|
|
LINKS
|
|
|
EXAMPLE
|
Number 12 is in the sequence because 12 divides 3*sigma(12) = 3*28.
|
|
MAPLE
|
select(n -> 3*numtheory:-sigma(n) mod n = 0, [$1..10^6]); # Robert Israel, Aug 26 2014
|
|
MATHEMATICA
|
a245774[n_Integer] := Select[Range[n], Divisible[3*DivisorSigma[1, #], #] == True &]; a245774[10^7] (* Michael De Vlieger, Aug 27 2014 *)
|
|
PROG
|
(Magma) [n: n in [1..3000000] | Denominator(3*(SumOfDivisors(n))/n) eq 1]
(PARI)
for(n=1, 10^9, if((3*sigma(n))%n==0, print1(n, ", "))) \\ Derek Orr, Aug 26 2014
|
|
CROSSREFS
|
Cf. A227303 (n divides sigma(3n)), A245775 (denominator(sigma(n)/n) = 3).
|
|
KEYWORD
|
nonn
|
|
AUTHOR
|
|
|
STATUS
|
approved
|
|
|
|