notice to mariners.
A square of an integer can never end with a digit that is 2,3,7 or 8.
can only end with a digit that is 0,1,4,5,6,9.
other hand, considering the last two digits can end only in these ways:
00
01, 21, 41, 61, 81
04, 24, 44, 64, 84 25
16, 36, 56, 76, 96
09, 29, 49, 69, 89.
So if you see a whole number that ends in one of these 22 ways, is not a true square, beware!