login
The OEIS Foundation is supported by donations from users of the OEIS and by a grant from the Simons Foundation.

 

Logo


Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
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

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 A275474

Adjacent sequences:  A277163 A277164 A277165 * A277167 A277168 A277169

KEYWORD

nonn

AUTHOR

Michel Lagneau, Oct 01 2016

STATUS

approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recent
The OEIS Community | Maintained by The OEIS Foundation Inc.

License Agreements, Terms of Use, Privacy Policy. .

Last modified September 18 16:22 EDT 2020. Contains 337170 sequences. (Running on oeis4.)