Determining whether a number is a Fibonacci number

Question

I need to to write a Java code that checks whether the user inputed number is in the Fibonacci sequence.

I have no issue writing the Fibonacci sequence to output, b

Answer 1

I don't know if there is an actual formula that you can apply to the user input however, you can generate the fibonacci sequence and check it against the user input until it has become smaller than the last number generated.

int userInput = n;
int a = 1, b = 1;

while (a < n) {
  if (a == n)
    return true;

  int next = a + b;
  b = a;
  a = next;
}

return false;