There's an answer here

http://www.mersenneforum.org/showthread.php?t=2007
you can not use 0 only 4 and can not use functions.

now that 51 is know, I will put a little program that I did to found it, and insert the double fatorial in its expressions to use.

between 0 to 100 still less to found abou 30 numbers. I think double fatorial will help a lot cause it's the only way to reach the number 3 using only 2 fours numbers.

1 = 4/4

2 = sqrt(4)

3 = 4!/4!!

5 = ?

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