21631320 has 64 divisors (see below), whose sum is σ = 72108000. Its totient is φ = 5768064.

The previous prime is 21631307. The next prime is 21631321. The reversal of 21631320 is 2313612.

21631320 is a `hidden beast` number, since 2 + 1 + 631 + 32 + 0 = 666.

It is a Harshad number since it is a multiple of its sum of digits (18).

It is a junction number, because it is equal to n+sod(n) for n = 21631293 and 21631302.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21631321) 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, 8935 + ... + 11094.

Almost surely, 2^21631320 is an apocalyptic number.

21631320 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21631320 is an abundant number, since it is smaller than the sum of its proper divisors (50476680).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

21631320 is a wasteful number, since it uses less digits than its factorization.

21631320 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 20049 (or 20039 counting only the distinct ones).

The product of its (nonzero) digits is 216, while the sum is 18.

The square root of 21631320 is about 4650.9482904027. The cubic root of 21631320 is about 278.6298710857.

Adding to 21631320 its reverse (2313612), we get a palindrome (23944932).

The spelling of 21631320 in words is "twenty-one million, six hundred thirty-one thousand, three hundred twenty".