Probably not as common as 1, 2, 3 or 5, there are still quite a few world coins which are denominated as 4 of something. Please post a coin worth 4 if you like. Here are a few to start: Japan Shin Kaneitsuhou 4 mon Papal States 1868 4 Soldi Austria 4 Kreuzer 1861 William IV 4 Pence (groat) 1836
This is a bit naughty as it's not quite a denomination but thought I'd post it here too Japan Akita Prefecture 1863 (ND) "4" monme 6 bu. I still find it fascinating as the number 4 is not well regarded in Japan (perhaps not as much as China) and yet it features on a coin.
This photo is off the internet but this coin came to mind for me when I saw the topic. One year issue from Germany.
A few more: Meklenburg-Strelitz 1849 4 Schillinge Georg 0.375 billon Corsica 4 Soldi 1764 Pasquale Paoli Spain Joseph Napoleon 4 Reales 1812 UK William III 1698 Groat (4 pence)
Another one: Germany Hamburg 4 Schillings 1728 Silver, 23 mm, 2.68 gm HAMBURGER CURRENT 1728 / IIII SCHILL The Hamburger Current (Courant) is the main type of coin in the Hamburg currency from 1725 to 1856. CAROLUS VI D.G. ROM IMP SEMP AVG / I.H. - L. Carolus VI Dei Gratia Romanorum Imperator Semper Augustus I.H.-L. is Johann Heinrich Löwe, Mint-master at Hamburg 1725-1760