21188631 has 4 divisors (see below), whose sum is σ = 28251512. Its totient is φ = 14125752.

The previous prime is 21188627. The next prime is 21188633. The reversal of 21188631 is 13688112.

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

It is not a de Polignac number, because 21188631 - 2² = 21188627 is a prime.

It is a super-2 number, since 2×21188631² = 897916167308322, 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 (21188633) 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, 3531436 + ... + 3531441.

It is an arithmetic number, because the mean of its divisors is an integer number (7062878).

Almost surely, 2^21188631 is an apocalyptic number.

21188631 is a deficient number, since it is larger than the sum of its proper divisors (7062881).

21188631 is an equidigital number, since it uses as much as digits as its factorization.

21188631 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 7062880.

The product of its digits is 2304, while the sum is 30.

The square root of 21188631 is about 4603.1110132170. Note that the first 3 decimals coincide. The cubic root of 21188631 is about 276.7160178733.

The spelling of 21188631 in words is "twenty-one million, one hundred eighty-eight thousand, six hundred thirty-one".