A "language" that has fibonacci builtin can do it 2 characters. fx. where f is the name of the fibonacci function and x is a single digit number.
A fibonacci DSL could do it in 1; if all input is expected to be an integral value and the machine only computes fibonacci values, then typing a single digit number would have the intended consequence:
A fibonacci DSL could do it in 1; if all input is expected to be an integral value and the machine only computes fibonacci values, then typing a single digit number would have the intended consequence: