1316891383625998382687 19326644346534830559 bytes

Brainfuck code:

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

Prints

28948022309329048855892746252171976963317496166410141009864396001978282409983 

null bytes.

19326644346528796447 bytes

Brainfuck code:

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

Prints

57896044618658097711785492504343953926634992332820282019728792003956564819967 

null bytes.

It works like this:

mem[i]=255; do while(--mem[i]){ mem[i+1]=mem[i+2]=mem[i]; mem[i]=1; i+=2; } while(mem[--i]); 

Quite straightforward recursion.

1316891383625998382687 bytes

Brainfuck code:

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

Prints

86844066927987146567678238756515930889952488499230423029593188005934847229950 

null bytes.

1316891383625998382687 19326644346534830559 bytes

Brainfuck code:

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

Prints

28948022309329048855892746252171976963317496166410141009864396001978282409983 

null bytes.