User blog comment:Deedlit11/Bignum Bakeoff appetizer/@comment-5529393-20140922180229

Same algorithm for Python:

i = 9 ** 9 ** 9 b = 2

def B(x,y): return y % b * (b+1)**B(0,x) + B(x+1,y/b) if y else 0

while i:	i = B(0,i)-1 b += 1 print b

91 characters.