21206331 has 6 divisors (see below), whose sum is σ = 30631380. Its totient is φ = 14137548.

The previous prime is 21206323. The next prime is 21206347. The reversal of 21206331 is 13360212.

It is not a de Polignac number, because 21206331 - 2³ = 21206323 is a prime.

It is a super-2 number, since 2×21206331² = 899416948963122, which contains 22 as substring.

It is not an unprimeable number, because it can be changed into a prime (21206131) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 1178121 + ... + 1178138.

It is an arithmetic number, because the mean of its divisors is an integer number (5105230).

Almost surely, 2^21206331 is an apocalyptic number.

21206331 is a deficient number, since it is larger than the sum of its proper divisors (9425049).

21206331 is a wasteful number, since it uses less digits than its factorization.

21206331 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2356265 (or 2356262 counting only the distinct ones).

The product of its (nonzero) digits is 216, while the sum is 18.

The square root of 21206331 is about 4605.0332246358. The cubic root of 21206331 is about 276.7930483388.

Adding to 21206331 its reverse (13360212), we get a palindrome (34566543).

The spelling of 21206331 in words is "twenty-one million, two hundred six thousand, three hundred thirty-one".