this formula x^2-x+41= Select 0,1,2,3,4 use these numbers for x substituting them in the formula and see if prime numbers occur. Try to find the number for x that when substituted in the formula yields a composite number.

this is a well known prime generating polynomial that produces primes for every integer less than 41. then at x=41 we get P(41)=41^2 (not a prime)