21071231 has 4 divisors (see below), whose sum is σ = 21359952. Its totient is φ = 20782512.

The previous prime is 21071221. The next prime is 21071249. The reversal of 21071231 is 13217012.

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

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21071231 is a prime.

It is a super-2 number, since 2×21071231² = 887993551710722, which contains 22 as substring.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21071221) 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 3 ways as a sum of consecutive naturals, for example, 144251 + ... + 144396.

It is an arithmetic number, because the mean of its divisors is an integer number (5339988).

Almost surely, 2^21071231 is an apocalyptic number.

21071231 is a deficient number, since it is larger than the sum of its proper divisors (288721).

21071231 is an equidigital number, since it uses as much as digits as its factorization.

21071231 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 288720.

The product of its (nonzero) digits is 84, while the sum is 17.

The square root of 21071231 is about 4590.3410548673. The cubic root of 21071231 is about 276.2040035893.

Adding to 21071231 its reverse (13217012), we get a palindrome (34288243).

The spelling of 21071231 in words is "twenty-one million, seventy-one thousand, two hundred thirty-one".