21256903 has 4 divisors (see below), whose sum is σ = 21556368. Its totient is φ = 20957440.

The previous prime is 21256867. The next prime is 21256909. The reversal of 21256903 is 30965212.

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-21256903 is a prime.

It is an alternating number because its digits alternate between even and odd.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21256909) 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, 149626 + ... + 149767.

It is an arithmetic number, because the mean of its divisors is an integer number (5389092).

Almost surely, 2^21256903 is an apocalyptic number.

21256903 is a deficient number, since it is larger than the sum of its proper divisors (299465).

21256903 is an equidigital number, since it uses as much as digits as its factorization.

21256903 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 299464.

The product of its (nonzero) digits is 3240, while the sum is 28.

The square root of 21256903 is about 4610.5209033253. The cubic root of 21256903 is about 277.0129019522.

It can be divided in two parts, 2 and 1256903, that added together give a triangular number (1256905 = T₁₅₈₅).

The spelling of 21256903 in words is "twenty-one million, two hundred fifty-six thousand, nine hundred three".