Problem 44 - Pentagonal numbers

 - Hard one!
 - Needed the internet's help on this one
 - My original solution had the loops organized differently to ensure
   the result was a minimum, but took too long to run:
 - foreach pentagonal d:
     foreach pentagonal a greater than d
       if b = d + a is pentagonal and a+b is pentagonal then return d
 - wouldn't terminate until d=5482660 in the outer loop :(