How many natural numbers from 1 to 1998 are squared by 72?
Because 72 = 23 × 32. As long as the multiplication number is twice the square number, the product is the complete square number. 1998 △ 2 = 999.312 = 961 < 999 < 322 = 1024, therefore, the square number less than 999 has 12, 22 312, a total of 31. Answer: there are 31 numbers multiplied by 72, which are complete square numbers
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