A277166 Numbers m such that m divides the number of divisors of m!!.

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

Offset

1,2

Comments

It seems that a(n) is asymptotic to c*n with c = 4.8...

Links

Amiram Eldar, Table of n, a(n) for n = 1..10000

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

Cf. A000005, A006882, A051178, A114338.

Sequence in context: A267894 A084345 A084561 * A078613 A072202 A354189

Adjacent sequences: A277163 A277164 A277165 * A277167 A277168 A277169

Keyword

nonn

Author

Michel Lagneau, Oct 01 2016

Status

approved