c=0
(Time.now..Time.gm(14)-1).step(86400){|d|p(d)if"#{d}"=~/F.{7}13/&&c+=1}
p c

# または同サイズの

c=0
(Time.now..Time.gm(14)-1).step(86400){|d|p(d)if d.day*d.wday==65&&c+=1}
p c