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A154893
Numbers whose number of proper divisors is not a prime number.
2
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
1,2
COMMENTS
Complement of A063806.
LINKS
MATHEMATICA
Select[Range[300], ! PrimeQ[DivisorSigma[0, # ] - 1] &] (* Stefan Steinerberger, Jan 31 2009 *)
PROG
(PARI) isok(n) = !isprime(numdiv(n)-1); \\ Michel Marcus, Apr 27 2018
CROSSREFS
Sequence in context: A167175 A026478 A211485 * A084111 A171474 A323520
KEYWORD
easy,nonn
AUTHOR
Omar E. Pol, Jan 25 2009
EXTENSIONS
More terms from Stefan Steinerberger, Jan 31 2009
STATUS
approved