21165266831 has 4 divisors (see below), whose sum is σ = 21165636072. Its totient is φ = 21164897592.

The previous prime is 21165266791. The next prime is 21165266851. The reversal of 21165266831 is 13866256112.

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 21165266831 - 2⁶ = 21165266767 is a prime.

It is a super-2 number, since 2×21165266831² (a number of 21 digits) 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 (21165266851) 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, 78185 + ... + 220098.

It is an arithmetic number, because the mean of its divisors is an integer number (5291409018).

Almost surely, 2^21165266831 is an apocalyptic number.

21165266831 is a deficient number, since it is larger than the sum of its proper divisors (369241).

21165266831 is an equidigital number, since it uses as much as digits as its factorization.

21165266831 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 369240.

The product of its digits is 103680, while the sum is 41.

The spelling of 21165266831 in words is "twenty-one billion, one hundred sixty-five million, two hundred sixty-six thousand, eight hundred thirty-one".