Oracle Software Developer IV interview questions

I was interviewed F2F 2 days ago and got update (on ask) from HR that I am rejected. It is a shock for me. There were two technical round, in first round there was only one question - finding a prime number, the formula of which I didn't remember and could not answer. Rest I replied everything excellently. In second round, it was 100% and the interviewer was impressed. I believe the first interviewer rejected me because of not replying exact formula of Prime Number. I felt, I performed outstanding ( I know I am overconfident) but I did that and since both interviewer were junior, the first one rejected me because of the fear.