# 1000-digit Fibonacci number

*Author: Flavio Poletti*

https://projecteuler.net/problem=25

The Fibonacci sequence is defined by the recurrence relation:

Fn = Fn1 + Fn2, where F1 = 1 and F2 = 1. Hence the first 12 terms will be:

F1 = 1 F2 = 1 F3 = 2 F4 = 3 F5 = 5 F6 = 8 F7 = 13 F8 = 21 F9 = 34 F10 = 55 F11 = 89 F12 = 144

The 12th term, F12, is the first term to contain three digits.

What is the first term in the Fibonacci sequence to contain 1000 digits?

Source code: prob025-polettix.pl

use v6; sub MAIN(Int :$length = 1000, Bool :$boring = False) { if $boring { my ($x, $y, $c) = (1, 1, 2); ($x, $y, $c) = ($y, $x + $y, $c + 1) while $y.chars < $length; $c.say; return; } my @fibs = 0, 1, *+* ... *; ((1..*).grep:{@fibs[$_].chars == $length})[0].say; return; }