

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
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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, (n1)\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



