Pan base non-primes: Difference between revisions

=={{header|Ruby}}==

<syntaxhighlight lang="ruby">require 'prime'

def int_from_digits(ar, base=10)

# expects array from digits method, which gives least significant digit first.

raise ArgumentError, "#{ar.max} not valid in base #{base}. " if ar.max > base-1

ar.each_with_index.sum {|d, i| d*base**i }

end

limit = 2500

a121719 = (2..limit).lazy.select do |n|

next false if (n < 10 && n.prime?)

digits = n.digits

from = digits.max + 1

(from..n).none?{|base| int_from_digits(digits, base).prime? }

end

n = 50

puts "First #{n} pan-base composites:"

a121719.take(n).each_slice(10){|s| puts "%4s"*s.size % s}

n = 20

puts "\nFirst #{n} odd pan-base composites:"

a121719.select(&:odd?).take(n).each_slice(10){|s| puts "%4s"*s.size % s }

tally = a121719.map(&:odd?).tally

total = tally.values.sum

puts "\nCount of pan-base composites up to and including #{limit}: #{total}"

puts "Number of odds is #{tally[true ]}, proportion #{tally[true ].fdiv(total) }%"

puts "Number of evens is #{tally[false]}, proportion #{tally[false].fdiv(total) }%"</syntaxhighlight>

{{out}}

<pre>First 50 pan-base composites:

4 6 8 9 20 22 24 26 28 30

33 36 39 40 42 44 46 48 50 55

60 62 63 64 66 68 69 70 77 80

82 84 86 88 90 93 96 99 100 110

112 114 116 118 120 121 130 132 134 136

First 20 odd pan-base composites:

9 33 39 55 63 69 77 93 99 121

143 165 169 187 231 253 273 275 297 299

Count of pan-base composites up to and including 2500: 953

Number of odds is 161, proportion 0.1689401888772298%

Number of evens is 792, proportion 0.8310598111227702%

</pre>