21255251 has 4 divisors (see below), whose sum is σ = 21265104. Its totient is φ = 21245400.

The previous prime is 21255239. The next prime is 21255257. The reversal of 21255251 is 15255212.

It is a semiprime because it is the product of two primes, and also a brilliant number, because the two primes have the same length.

It is a cyclic number.

It is not a de Polignac number, because 21255251 - 2¹⁰ = 21254227 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21255257) 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, 140 + ... + 6521.

It is an arithmetic number, because the mean of its divisors is an integer number (5316276).

Almost surely, 2^21255251 is an apocalyptic number.

21255251 is a deficient number, since it is larger than the sum of its proper divisors (9853).

21255251 is an equidigital number, since it uses as much as digits as its factorization.

21255251 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 9852.

The product of its digits is 1000, while the sum is 23.

The square root of 21255251 is about 4610.3417443829. The cubic root of 21255251 is about 277.0057256611.

The spelling of 21255251 in words is "twenty-one million, two hundred fifty-five thousand, two hundred fifty-one".