A154893 Numbers whose number of proper divisors is not a prime number.
1, 2, 3, 5, 7, 11, 13, 16, 17, 19, 23, 29, 31, 36, 37, 41, 43, 47, 48, 53, 59, 61, 64, 67, 71, 73, 79, 80, 81, 83, 89, 97, 100, 101, 103, 107, 109, 112, 113, 120, 127, 131, 137, 139, 144, 149, 151, 157, 162, 163, 167, 168, 173, 176, 179, 181, 191, 193, 196, 197, 199
Offset: 1
Links
- Shawn A. Broyles, Table of n, a(n) for n = 1..10000
Programs
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Mathematica
Select[Range[300], ! PrimeQ[DivisorSigma[0, # ] - 1] &] (* Stefan Steinerberger, Jan 31 2009 *)
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PARI
isok(n) = !isprime(numdiv(n)-1); \\ Michel Marcus, Apr 27 2018
Extensions
More terms from Stefan Steinerberger, Jan 31 2009
Comments