21391725 has 24 divisors (see below), whose sum is σ = 36908352. Its totient is φ = 10912000.

The previous prime is 21391723. The next prime is 21391751. The reversal of 21391725 is 52719312.

It is not a de Polignac number, because 21391725 - 2¹ = 21391723 is a prime.

It is a Curzon number.

It is a junction number, because it is equal to n+sod(n) for n = 21391692 and 21391701.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21391723) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 4476 + ... + 7925.

It is an arithmetic number, because the mean of its divisors is an integer number (1537848).

Almost surely, 2^21391725 is an apocalyptic number.

21391725 is a gapful number since it is divisible by the number (25) formed by its first and last digit.

It is an amenable number.

21391725 is a deficient number, since it is larger than the sum of its proper divisors (15516627).

21391725 is a wasteful number, since it uses less digits than its factorization.

21391725 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 12437 (or 12432 counting only the distinct ones).

The product of its digits is 3780, while the sum is 30.

The square root of 21391725 is about 4625.1189173901. The cubic root of 21391725 is about 277.5973199765.

The spelling of 21391725 in words is "twenty-one million, three hundred ninety-one thousand, seven hundred twenty-five".