How many perfect squares are of the form shown in the formula above?
This section requires Javascript.
You are seeing this because something didn't load right. We suggest you, (a) try
refreshing the page, (b) enabling javascript if it is disabled on your browser and,
finally, (c)
loading the
non-javascript version of this page
. We're sorry about the hassle.
Relevant wiki: Perfect Squares, Cubes, and Powers
From 1 0 1 1 0 1 ≤ n 2 ≤ 1 0 9 9 0 9 it follows by taking square roots that 3 1 8 ≤ n ≤ 3 3 1 . We can rule out 3 2 0 and 3 3 0 immediately because their squares would end in zero; and 3 2 5 because its square would end in 2 5 .
For the remaining 11 numbers, it helps to know that the last two digits of the square is equal to the last two digits of the square of the last two digits; e.g. 3 1 8 2 ≡ 1 8 2 ≡ 2 4 mod 100, etc.
As it turns out, none of the squares of these numbers has a zero at the tens position. Therefore the answer is zero, zilch, zip, naught, nada .