拡張素数日

primedate.rb

#!/usr/bin/ruby
#
# Copyright 2023 zunda <zundan at gmail.com>
#
# Permission is granted for use, copying, modification, distribution,
# and distribution of modified versions of this work as long as the
# above copyright notice is included.
#
require 'prime'

today = Time.now.localtime.strftime('%Y%m%d')
a = today.scan(/\d/).map{|i| i.to_i}.reverse
b = a.max + 1
r = nil
while b < 100
  if a.map.with_index{|n,i| n*b**i}.sum.prime?
    r = "今日#{today}は基数#{b}で素数だからがんばろう"
    break
  end
  b += 1
end
r ||= "今日#{today}は素数日じゃないかもしれない"
puts r