Sometimes it’s easy, sometimes it’s not: Developing a visual pun. For 2013’s New Year’s card is was some kind of obvious to combine the two changing digits of the years and thereby express the change in a typographic manner.
Yet only a very few letter forms allow this creation of a horizontal ligature. Apart from 2 and 3 only the combination of 8 and 9 is a similarly natural fit. Of course one might able to force some other numbers into a fusion – or be another Herb Lubalin and do calligraphic magic.