It is: 4
There are three perfect squares between 0 and 50 that are even.
8, 10 24, 26
3 is prime, 1 less than the perfect square of 4 (2x2)
256 is the greatest even square number that is less than 300.
One way is to get the prime factorization of the number. If every prime occurs an even number of times, it is a square, otherwise, not. Another is to estimate the square root of the number, and square it. If you get more than the number, try a lower estimate; if less, a higher one. Using interval bisection you very quickly zero in on the square root, if it is a whole number. If so, the number is a perfect square. Otherwise, you find 2 consecutive whole numbers between which is the square root, in which case it is not a perfect square.
A square number, or perfect square, is the square of an integer. 232 is less than 572, 242 is more, so it is not the square of an integer.
It is 64 which is also a square number
There is only one even prime number and that is 2 as all over even numbers can be divided by 2 and 2 is not square so there isn't a number less than 100 that is an even prime square number.
4
Every non-negative real number is a square (every number if in the complex field) so every real number greater than or equal to -1 is one less than a square. Even if you restrict yourself to perfect squares, of the form n2, then n2 - 1 = (n-1)*(n+1) is one less than a square. There are infinitely many such numbers.
1,0002 = 1,000,000 so 1 less is 9992 = 998,001
Any number squared except 0 is a perfect square so it follows that prime numbers are less common than perfect squares.