21187631 has 4 divisors (see below), whose sum is σ = 21340200. Its totient is φ = 21035064.

The previous prime is 21187619. The next prime is 21187633. The reversal of 21187631 is 13678112.

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 21187631 - 2⁶ = 21187567 is a prime.

It is a super-2 number, since 2×21187631² = 897831414784322, which contains 22 as substring.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 21187594 and 21187603.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21187633) 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, 76076 + ... + 76353.

It is an arithmetic number, because the mean of its divisors is an integer number (5335050).

Almost surely, 2^21187631 is an apocalyptic number.

21187631 is a deficient number, since it is larger than the sum of its proper divisors (152569).

21187631 is a wasteful number, since it uses less digits than its factorization.

21187631 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 152568.

The product of its digits is 2016, while the sum is 29.

The square root of 21187631 is about 4603.0023897452. The cubic root of 21187631 is about 276.7116645895.

The spelling of 21187631 in words is "twenty-one million, one hundred eighty-seven thousand, six hundred thirty-one".