21242725 has 18 divisors (see below), whose sum is σ = 30643314. Its totient is φ = 14565600.

The previous prime is 21242717. The next prime is 21242729. The reversal of 21242725 is 52724212.

It can be written as a sum of positive squares in 3 ways, for example, as 4588164 + 16654561 = 2142^2 + 4081^2 .

It is not a de Polignac number, because 21242725 - 2³ = 21242717 is a prime.

It is a Harshad number since it is a multiple of its sum of digits (25).

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 21242725.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21242729) by changing a digit.

It is a polite number, since it can be written in 17 ways as a sum of consecutive naturals, for example, 7446 + ... + 9895.

Almost surely, 2^21242725 is an apocalyptic number.

21242725 is a gapful number since it is divisible by the number (25) formed by its first and last digit.

It is an amenable number.

21242725 is a deficient number, since it is larger than the sum of its proper divisors (9400589).

21242725 is a wasteful number, since it uses less digits than its factorization.

21242725 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 17365 (or 17353 counting only the distinct ones).

The product of its digits is 2240, while the sum is 25.

The square root of 21242725 is about 4608.9830765582. The cubic root of 21242725 is about 276.9513005916.

Adding to 21242725 its reverse (52724212), we get a palindrome (73966937).

The spelling of 21242725 in words is "twenty-one million, two hundred forty-two thousand, seven hundred twenty-five".