The 17th term is 50C16*2^34*a^16
The 18th term is 50C17*2^33*a^17
The ratio of these two terms is (17th term)/(18th term) = 1/a. We want the value of this to be 1, so
.. A = 1
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My calculator says
.. 50C16 = 4,923,689,695,575
.. 50C17 = 9,847,379,391,150
the latter being exactly 2 times the former.
