Numbers whose count of divisors is prime

var limit = 100_000
say "Positive integers under #{limit.commify} whose number of divisors is an odd prime:"
 
1..limit -> grep { !.is_prime && .sigma0.is_prime }.each_slice(10, {|*a|
    say a.map{'%6s' % _}.join(' ')
})

Output:

Positive integers under 100,000 whose number of divisors is an odd prime:
     4      9     16     25     49     64     81    121    169    289
   361    529    625    729    841    961   1024   1369   1681   1849
  2209   2401   2809   3481   3721   4096   4489   5041   5329   6241
  6889   7921   9409  10201  10609  11449  11881  12769  14641  15625
 16129  17161  18769  19321  22201  22801  24649  26569  27889  28561
 29929  32041  32761  36481  37249  38809  39601  44521  49729  51529
 52441  54289  57121  58081  59049  63001  65536  66049  69169  72361
 73441  76729  78961  80089  83521  85849  94249  96721  97969