login
A354768
Numbers k such that d(k)/k >= d(m)/m for all m > k, where d(k) is the number-of-divisors function A000005(k).
4
1, 2, 4, 6, 8, 12, 18, 24, 30, 36, 48, 60, 72, 84, 90, 120, 144, 180, 240, 252, 360, 420, 480, 504, 540, 720, 840, 900, 1008, 1080, 1260, 1440, 1680, 1800, 2520, 2640, 2880, 3360, 3780, 3960, 5040, 5280, 5400, 5460, 5544, 6300, 7560, 7920, 8400, 10080, 10920, 12600, 15120, 15840, 16380, 18480
OFFSET
1,2
COMMENTS
Because of the bound d(m) <= 2*sqrt(m), in order for k to be in the sequence it suffices that d(k)/k >= d(m)/m for k < m < (2*k/d(k))^2. - Robert Israel, Jan 23 2023
REFERENCES
David desJardins, Posting to Math Fun Mailing List, Jun 21 2022.
MAPLE
N:= 10^6:
Q:= [seq(numtheory:-tau(k)/k, k=1..N)]:
V:= Vector(10^6):
r:= 2/10^3:
for n from 10^6 to 1 by -1 do
r:= max(Q[n], r);
V[n]:= r;
od:
select(i -> Q[i] >= V[i+1], [$1..10^6-1]); # Robert Israel, Jan 23 2023
CROSSREFS
KEYWORD
nonn
AUTHOR
N. J. A. Sloane, Jun 21 2022
EXTENSIONS
More terms from Robert Israel, Jan 23 2023
STATUS
approved