1.8602094114556065622...

This number is neither prime nor composite.

       1.8 6020941145 5606562291 7319762082 1862473898 9898760358 6557719830
0876661746 5111786158 2811869872 7975999968 1851439945 2150716341 2228450005
9105492443 9600917588 6782699100 0461245695 4063414986 2496487392 8008573...

The value of the infinite exponent: (2^1/2)^((3^1/3)^((5^1/5)^((7^1/7)^...) taken over the set of all primes. [Rupinski]