[docs] [issue31757] Tutorial: Fibonacci numbers start with 1, 1

Mark Dickinson report at bugs.python.org
Wed Oct 11 12:07:56 EDT 2017

Mark Dickinson <dickinsm at gmail.com> added the comment:

Is there any particular reason you want to start with 1? While not universal, it's standard to define `Fib(0) = 0`, and to start the sequence at `0`. (And note that Python usually starts indexing things from 0, so it makes sense to start with `Fib(0)` rather than `Fib(1)`.)

In principle, one could define `Fib(0)=1`, `Fib(1)=1`, `Fib(1)=2`, and so on, but there's a strong reason not to do so: it breaks (or at least uglifies) many nice number-theoretic properties, like `gcd(Fib(m), Fib(n)) == Fib(gcd(m, n))`.

nosy: +mark.dickinson

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