DouKaku?

#!/usr/bin/env ruby
require 'date'

from = DateTime.now
to = DateTime.parse("2013-12-31")

friday = (from..to).inject(0) do |friday, date|
    if date.mday == 13 and date.wday == 5 then
        puts date.strftime('%Y-%m-%d')
        friday + 1
    else
        friday
    end
end

puts friday

private import std.stdio, std.date;

enum Friday = 5;

void main(){
    auto count = 0;
    foreach(day; Day(getUTCtime) .. MakeDay(2014, 1, 1)) {
        auto date = MakeDate(day, 0);
        if(WeekDay(date) == Friday && DateFromTime(date) == 13) {
            writefln("%04d-%02d-%02d", YearFromTime(date), MonthFromTime(date) + 1, DateFromTime(date));
            ++count;
        }
    }
    writeln(count);
}