621
xkcd #2922: Pub Trivia
(imgs.xkcd.com)
Alt text:
Bonus question: Where is London located? (a) The British Isles (b) Great Britain and Northern Ireland (c) The UK (d) Europe (or 'the EU') (e) Greater London
1+4=5 not 4 and 4 isn't prime either, so idk what you meant. 4 is the sum of two primes 2+2, which I thought was what you were asking at first.
I screwed up twice here. Forgot 2 was a prime somehow.
1+4 was just a typo, meant 1+3.