21213231 has 8 divisors (see below), whose sum is σ = 30460080. Its totient is φ = 13054272.

The previous prime is 21213193. The next prime is 21213251. The reversal of 21213231 is 13231212.

It is a sphenic number, since it is the product of 3 distinct primes.

It is not a de Polignac number, because 21213231 - 2¹³ = 21205039 is a prime.

It is a super-2 number, since 2×21213231² = 900002338918722, which contains 22 as substring.

It is a self number, because there is not a number n which added to its sum of digits gives 21213231.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21213251) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 271926 + ... + 272003.

It is an arithmetic number, because the mean of its divisors is an integer number (3807510).

Almost surely, 2^21213231 is an apocalyptic number.

21213231 is a deficient number, since it is larger than the sum of its proper divisors (9246849).

21213231 is a wasteful number, since it uses less digits than its factorization.

21213231 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 543945.

The product of its digits is 72, while the sum is 15.

The square root of 21213231 is about 4605.7823439672. The cubic root of 21213231 is about 276.8230655529.

Adding to 21213231 its reverse (13231212), we get a palindrome (34444443).

The spelling of 21213231 in words is "twenty-one million, two hundred thirteen thousand, two hundred thirty-one".