Create 025.js

Author: Walker30263

025.js

@@ -0,0 +1,18 @@
+//function that returns F_n where F_1 = 1, F_2 = 1, F_3 = 2, F_4 = 3, etc.
+function fibonacci(n) {
+  let fibonacci = [1n, 1n]; //create an array of first 2 terms in the sequence
+
+  while (fibonacci.length < n) {
+    fibonacci.push(fibonacci[BigInt(fibonacci.length)-1n] + fibonacci[BigInt(fibonacci.length)-2n]) //push the sum of the last 2 terms, because that's the fibonacci sequence rule
+  }
+
+  return fibonacci[BigInt(fibonacci.length)-1n]; //return the last element of the array since it's the nth fibonacci number
+}
+
+let index = 1n;
+
+while (fibonacci(index).toString().length < 1000) { //keep generating fibonacci numbers until there's one that's 1000 digits long
+  index++;
+}
+
+console.log(index); //outputs answer