A number `n` is said to be perfect if the sum of all its divisors (excluding `n` itself) is equal to `n` . An example of perfect number is (a) 6 (b) 9 (c) 15 (d) 21

A number is said to be a nice number if it has exactly 4 factors (includng 1 and the number itself). Then number of divisor of 2520 which are nice numbers is (A) 7 (B) 8 (C) 9 (D) none of these

A number is said to be a nice number if it has exactly 4 factors (includng 1 and the number itself). Then number of divisor of 2520 which are nice numbers is (A) 7 (B) 8 (C) 9 (D) none of these

The smallest positive integer n, for which 864n is a perfect cube,is (a) 1 (b) 2 (c) 3 (d) 4

We call a number perfect if it is the sum of all its positive divisors, except itself. e.g. 28 is a perfect number because 28=1+2+4+7+14 . Which of the following numbers is a perfect number?

What is sqrt(n) if n is not a perfect square number?

PERFECT NUMBERS If the sum of all the factors of a number is two xx the number then the number is called a perfect number.

If the n^(th) term of an A.P.is (2n+1), then the sum of its first three terms is (a) 6n+3 (b) 15 (c) 12 (d) 21