21253645 has 16 divisors (see below), whose sum is σ = 29479680. Its totient is φ = 14408064.

The previous prime is 21253627. The next prime is 21253649. The reversal of 21253645 is 54635212.

It is a cyclic number.

It is not a de Polignac number, because 21253645 - 2⁵ = 21253613 is a prime.

It is a super-3 number, since 3×21253645³ (a number of 23 digits) contains 333 as substring.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21253649) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 297 + ... + 6526.

It is an arithmetic number, because the mean of its divisors is an integer number (1842480).

Almost surely, 2^21253645 is an apocalyptic number.

It is an amenable number.

21253645 is a deficient number, since it is larger than the sum of its proper divisors (8226035).

21253645 is an equidigital number, since it uses as much as digits as its factorization.

21253645 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 6924.

The product of its digits is 7200, while the sum is 28.

The square root of 21253645 is about 4610.1675674535. The cubic root of 21253645 is about 276.9987488377.

Adding to 21253645 its reverse (54635212), we get a palindrome (75888857).

The spelling of 21253645 in words is "twenty-one million, two hundred fifty-three thousand, six hundred forty-five".