21820231 has 4 divisors (see below), whose sum is σ = 23103792. Its totient is φ = 20536672.

The previous prime is 21820213. The next prime is 21820243. The reversal of 21820231 is 13202812.

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 21820231 - 2⁷ = 21820103 is a prime.

It is a super-2 number, since 2×21820231² = 952244961786722, 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 = 21820199 and 21820208.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21880231) 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, 641755 + ... + 641788.

It is an arithmetic number, because the mean of its divisors is an integer number (5775948).

Almost surely, 2^21820231 is an apocalyptic number.

21820231 is a deficient number, since it is larger than the sum of its proper divisors (1283561).

21820231 is a wasteful number, since it uses less digits than its factorization.

21820231 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1283560.

The product of its (nonzero) digits is 192, while the sum is 19.

The square root of 21820231 is about 4671.2130116277. The cubic root of 21820231 is about 279.4386329303.

It can be divided in two parts, 218 and 20231, that added together give a square (20449 = 143²).

The spelling of 21820231 in words is "twenty-one million, eight hundred twenty thousand, two hundred thirty-one".