public static BigNumber Fibonacci(int n) { BigNumber a = new BigNumber(0); BigNumber b = new BigNumber(1); int nr = 2; if (n <= 1) { return(a); } if (n == 2) { return(b); } while (nr < n) { nr++; BigNumber c = a + b; a = b.Clone(); b = c.Clone(); } return(b); }