The squares of natural numbers form a line from small to large to form a number: 1491623649 What's the number at position 800?

The squares of natural numbers form a line from small to large to form a number: 1491623649 What's the number at position 800?

Square is a natural number of one digit, 1-3, each occupying one digit, 1 * 3 = 3
Square is a natural number of 2 digits, 4-9, each occupying 2 digits, 2 * 6 = 12
Square is a natural number of 3 digits, 10-31, 3 digits each, 3 * 22 = 66
Square is a natural number with 4 digits, 32-99, each with 4 digits, 4 * 68 = 272
Square is a natural number with 5 digits, 100-316, each with 5 digits, 5 * 217 = 1085 > 800
（3+12+66+272＝353）
Request 800, now 353 has finished 4 digits
There are still 800-353 = 447, with the square equal to 5 digits, each occupying 5 digits. 447 / 5 = 89, and the remainder is 2
It is the 90th number of the fifth kind, which is 189
189 * 189 = 35721, we can see that the number is 5