21240725 has 12 divisors (see below), whose sum is σ = 28733280. Its totient is φ = 15447600.

The previous prime is 21240719. The next prime is 21240743. The reversal of 21240725 is 52704212.

It is a happy number.

It is a de Polignac number, because none of the positive numbers 2^k-21240725 is a prime.

It is a Curzon number.

It is a self number, because there is not a number n which added to its sum of digits gives 21240725.

It is a congruent number.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 38345 + ... + 38894.

It is an arithmetic number, because the mean of its divisors is an integer number (2394440).

Almost surely, 2^21240725 is an apocalyptic number.

21240725 is a gapful number since it is divisible by the number (25) formed by its first and last digit.

It is an amenable number.

21240725 is a deficient number, since it is larger than the sum of its proper divisors (7492555).

21240725 is a wasteful number, since it uses less digits than its factorization.

21240725 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 77260 (or 77255 counting only the distinct ones).

The product of its (nonzero) digits is 1120, while the sum is 23.

The square root of 21240725 is about 4608.7661038504. The cubic root of 21240725 is about 276.9426086750.

Adding to 21240725 its reverse (52704212), we get a palindrome (73944937).

The spelling of 21240725 in words is "twenty-one million, two hundred forty thousand, seven hundred twenty-five".