I have this system of equation, and I had to do the same thing using recursion in C#, so I came up with this :

public static long F1(int n) { if (n > 1) return F1(n - 2) + 10 * (long)Math.Pow(F1(n/6),2) + 6 * F1(n / 7) + ((long)Math.Pow(n,4) / 5); else return 2; }

I need help calculating the time complexity of this algorithm, and I don't even know where to start and how to do it, could you please give me a hand?

Thank you for any kind of help.