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- #!/usr/bin/ruby
- # Daniel "Trizen" Șuteu
- # Date: 13 March 2021
- # https://github.com/trizen
- # Generate k-omega primes in range [a,b]. (not in sorted order)
- # Definition:
- # k-omega primes are numbers n such that omega(n) = k.
- # See also:
- # https://en.wikipedia.org/wiki/Almost_prime
- # https://en.wikipedia.org/wiki/Prime_omega_function
- func omega_prime_numbers(a, b, k, callback) {
- a = max(k.pn_primorial, a)
- func (m, lo, k) {
- var hi = idiv(b,m).iroot(k)
- if (lo > hi) {
- return nil
- }
- each_prime(lo, hi, {|p|
- for (var t = m*p ; t <= b; t *= p) {
- if (k == 1) {
- callback(t) if (t >= a)
- }
- else {
- __FUNC__(t, p+1, k-1) if (t*p <= b)
- }
- }
- })
- }(1, 2, k)
- return callback
- }
- # Generate 5-omega primes in the range [3000, 10000]
- var k = 5
- var from = 3000
- var upto = 10000
- var arr = gather {
- omega_prime_numbers(from, upto, k, { take(_) })
- }.sort
- assert_eq(arr, max(from, k.pn_primorial)..upto -> grep{ .omega == k })
- say arr
- # Run some tests
- for k in (1..6) {
- var from = k.pn_primorial+1e3.irand
- var upto = from+1e4.irand
- say "Testing: #{k} with #{from} .. #{upto}"
- var arr = gather {
- omega_prime_numbers(from, upto, k, { take(_) })
- }.sort
- assert_eq(arr, max(from, k.pn_primorial)..upto -> grep{ .omega == k })
- }
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