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
Keywords
Examples
8 is in the sequence because the number of divisor of 8!! is A114338(8) = 16, which is divisible by 8.
Links
- Amiram Eldar, Table of n, a(n) for n = 1..10000
Programs
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Mathematica
ok[n_] := Divisible[ DivisorSigma[0, n!!], n]; Select[ Range[200], ok]
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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
Formula
A114338(a(n)) mod a(n) = 0.
Comments