Largest Number in Brainfuck BigInt for each program length up to 50 instructions

(²⁶2)-2

+++++[->+++++<]>[->+[->+[->++<]>[-<+>]<<]<[->+<]>]

Where (⁴2) = 2²²²

f²⁰(0), where f(x):=(4^x+2-4)/3

++++[->+++++<]>[->+[->+[->++<]>[-<++>]<<]<[->+<]>]