21857631 has 16 divisors (see below), whose sum is σ = 31578624. Its totient is φ = 13394304.

The previous prime is 21857621. The next prime is 21857651. The reversal of 21857631 is 13675812.

It is not a de Polignac number, because 21857631 - 2⁹ = 21857119 is a prime.

It is a super-2 number, since 2×21857631² = 955512065864322, which contains 22 as substring.

It is a junction number, because it is equal to n+sod(n) for n = 21857592 and 21857601.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21857621) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 2791 + ... + 7176.

It is an arithmetic number, because the mean of its divisors is an integer number (1973664).

Almost surely, 2^21857631 is an apocalyptic number.

21857631 is a deficient number, since it is larger than the sum of its proper divisors (9720993).

21857631 is a wasteful number, since it uses less digits than its factorization.

21857631 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 10030.

The product of its digits is 10080, while the sum is 33.

The square root of 21857631 is about 4675.2145405318. The cubic root of 21857631 is about 279.5981949368.

The spelling of 21857631 in words is "twenty-one million, eight hundred fifty-seven thousand, six hundred thirty-one".