21256243 has 4 divisors (see below), whose sum is σ = 21604768. Its totient is φ = 20907720.

The previous prime is 21256229. The next prime is 21256247. The reversal of 21256243 is 34265212.

It is a semiprime because it is the product of two primes.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21256243 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21256247) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 174171 + ... + 174292.

It is an arithmetic number, because the mean of its divisors is an integer number (5401192).

Almost surely, 2^21256243 is an apocalyptic number.

21256243 is a deficient number, since it is larger than the sum of its proper divisors (348525).

21256243 is an equidigital number, since it uses as much as digits as its factorization.

21256243 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 348524.

The product of its digits is 2880, while the sum is 25.

The square root of 21256243 is about 4610.4493273433. The cubic root of 21256243 is about 277.0100349556.

The spelling of 21256243 in words is "twenty-one million, two hundred fifty-six thousand, two hundred forty-three".