Data update

Task/Achilles-numbers/Ruby/achilles-numbers.rb

@@ -0,0 +1,23 @@
+require 'prime'
+
+def achilles?(n)
+  exponents = n.prime_division.map(&:last)
+  exponents.none?(1) && exponents.inject(&:gcd) == 1
+end
+
+def 𝜑(n)
+  n.prime_division.inject(1){|res, (pr, exp)| res * (pr-1) * pr**(exp-1) }
+end
+
+achilleses =  (2..).lazy.select{|n| achilles?(n) }
+
+n = 50
+puts "First #{n} Achilles numbers:"
+achilleses.first(n).each_slice(10){|s| puts "%9d"*s.size % s}
+
+puts "\nFirst #{n} strong Achilles numbers:"
+achilleses.select{|ach| achilles?(𝜑(ach)) }.first(n).each_slice(10){|s| puts "%9d"*s.size % s }
+
+puts
+counts = achilleses.take_while{|ach| ach < 1000000}.map{|a| a.digits.size }.tally
+counts.each{|k, v| puts "#{k} digits: #{v}" }