21806253 has 20 divisors (see below), whose sum is σ = 37229280. Its totient is φ = 12460392.

The previous prime is 21806227. The next prime is 21806263. The reversal of 21806253 is 35260812.

It is not a de Polignac number, because 21806253 - 2⁸ = 21805997 is a prime.

It is a Harshad number since it is a multiple of its sum of digits (27).

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21806263) by changing a digit.

It is a polite number, since it can be written in 19 ways as a sum of consecutive naturals, for example, 18663 + ... + 19796.

It is an arithmetic number, because the mean of its divisors is an integer number (1861464).

Almost surely, 2^21806253 is an apocalyptic number.

It is an amenable number.

21806253 is a deficient number, since it is larger than the sum of its proper divisors (15423027).

21806253 is an equidigital number, since it uses as much as digits as its factorization.

21806253 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 38478 (or 38469 counting only the distinct ones).

The product of its (nonzero) digits is 2880, while the sum is 27.

The square root of 21806253 is about 4669.7165866892. The cubic root of 21806253 is about 279.3789508923.

The spelling of 21806253 in words is "twenty-one million, eight hundred six thousand, two hundred fifty-three".