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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).
Supersequence of A007691 and A245775.
Union of A007691 and 3*A227303. - Robert Israel, Aug 26 2014
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. A000203 (sum of divisors), A007691 (multiply-perfect numbers).
Cf. A227303 (n divides sigma(3n)), A245775 (denominator(sigma(n)/n) = 3).
Cf. A272027 (3*sigma(n)).
Sequence in context: A292290 A018011 A025208 * A369148 A049941 A219634
KEYWORD
nonn
AUTHOR
Jaroslav Krizek, Aug 26 2014
STATUS
approved

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Last modified July 18 10:00 EDT 2024. Contains 374378 sequences. (Running on oeis4.)