function recursion(n, level = 0) {
recursion.count += 1;
const tab = '\t'.repeat(level);
console.log(`${tab}n=${n}, count=${recursion.count}`);
if (n < 1) return;
recursion(n - 1, level + 1);
recursion(n - 2, level + 1);
}
// a(n): recursion count
// a(-1) = 1, a(0) = 1,
// a(n) = a(n-1) + a(n-2) + 1 , n>=1
// n: -1 0 1 2 3 4 5
// -----------------------
// a(n): 1 1 3 5 9 15 25
recursion.count = 0;
recursion(5);
;[
recursion.count, // 25
].forEach(x => console.log(x));
