according to the official site, 42 entrants this year (including those who didn't get out of the semifinals - just fyi the UK has large enough viewing figures to ensure they avoid the semis altogether)
51 countries have entered in the history of the competition.
4 countries eligible to enter have withdrawn due to their own reasons, some to do with Israel's involvement.
Also, Algeria, Lybia, Egypt and Jordan are eligible as members of the EBU, but have neve taken part.
So - 59 total.