User blog comment:Maxywaxy/Fast growing function i created?/@comment-30869823-20190106194557

For some reason I thought : "hmmm I could program this in brainfuck" and actually did it:

Without unneasecairy charaters (128 characters)

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

Explanation:

S=0 >>, take input [ WHILE the first entry isn't zero <<+ INC S  [>>[>]>+>+<<<[<]<-] >>[>]>>[<<<[<]<+>>[>]>>-]< COPY S past the last entry (T) <<-  DEC the last entry (A) [>+>>+<<<-]>[<+>-]  >>[[-]  IF A'      <[ WHILE T          [>+<-] move T one to the right          <<[>+>+<<-]>>[<<+>>-] copy A          >- DEC T      ]  >] <[-] T=0 <<<[<]>] GOTO the first entry to make the loop work <<. OUTPUT S