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A277166 Numbers m such that m divides the number of divisors of m!!. 2
1, 2, 4, 8, 15, 16, 24, 27, 32, 36, 40, 48, 54, 56, 60, 63, 64, 72, 80, 84, 90, 96, 104, 105, 108, 112, 120, 128, 132, 135, 140, 144, 147, 152, 156, 160, 164, 165, 168, 180, 189, 192, 195, 200, 204, 210, 216, 220, 224, 225, 228, 231, 240, 243, 250, 252, 256 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,2
COMMENTS
It seems that a(n) is asymptotic to c*n with c = 4.8...
LINKS
FORMULA
A114338(a(n)) mod a(n) = 0.
EXAMPLE
8 is in the sequence because the number of divisor of 8!! is A114338(8) = 16, which is divisible by 8.
MATHEMATICA
ok[n_] := Divisible[ DivisorSigma[0, n!!], n]; Select[ Range[200], ok]
PROG
(PARI) isok(n) = (numdiv(prod(i=0, (n-1)\2, n - 2*i)) % n) == 0; \\ after first Pari in A006882; Michel Marcus, Oct 02 2016
CROSSREFS
Sequence in context: A267894 A084345 A084561 * A078613 A072202 A354189
KEYWORD
nonn
AUTHOR
Michel Lagneau, Oct 01 2016
STATUS
approved

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Last modified July 25 06:58 EDT 2024. Contains 374586 sequences. (Running on oeis4.)