21811231 has 4 divisors (see below), whose sum is σ = 23489032. Its totient is φ = 20133432.

The previous prime is 21811211. The next prime is 21811261. The reversal of 21811231 is 13211812.

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

It is a cyclic number.

It is not a de Polignac number, because 21811231 - 2¹³ = 21803039 is a prime.

It is a super-2 number, since 2×21811231² = 951459595470722, which contains 22 as substring.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 21811199 and 21811208.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21811211) 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, 838881 + ... + 838906.

It is an arithmetic number, because the mean of its divisors is an integer number (5872258).

Almost surely, 2^21811231 is an apocalyptic number.

21811231 is a deficient number, since it is larger than the sum of its proper divisors (1677801).

21811231 is a wasteful number, since it uses less digits than its factorization.

21811231 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1677800.

The product of its digits is 96, while the sum is 19.

The square root of 21811231 is about 4670.2495650661. The cubic root of 21811231 is about 279.4002084432.

It can be divided in two parts, 218 and 11231, that added together give a square (11449 = 107²).

The spelling of 21811231 in words is "twenty-one million, eight hundred eleven thousand, two hundred thirty-one".