Let N= 2^2 \times 3^3 \times 7^4. How many factors of N^2 which are less than N,are not factors of N
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Given that
N = 2 2 × 3 3 × 7 4
⇒ N 2 = 2 4 × 3 6 × 7 8
Number of positive factors of N = ( 2 + 1 ) ( 3 + 1 ) ( 4 + 1 ) = 6 0
Number of positive factors of N 2 = ( 4 + 1 ) ( 6 + 1 ) ( 8 + 1 ) = 3 1 5 which includes N and half each of remaining as < N and > N .
Number of positive factors of N 2 which are ≤ N = ( 3 1 5 + 1 ) / 2 = 1 5 8
Number of positive factors of N 2 which are less than N ,are not factors of N = 1 5 8 − 6 0 = 9 8