21315820 has 12 divisors (see below), whose sum is σ = 44763264. Its totient is φ = 8526320.

The previous prime is 21315803. The next prime is 21315821. The reversal of 21315820 is 2851312.

It is a junction number, because it is equal to n+sod(n) for n = 21315791 and 21315800.

It is not an unprimeable number, because it can be changed into a prime (21315821) 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, 532876 + ... + 532915.

It is an arithmetic number, because the mean of its divisors is an integer number (3730272).

Almost surely, 2^21315820 is an apocalyptic number.

21315820 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21315820 is an abundant number, since it is smaller than the sum of its proper divisors (23447444).

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

21315820 is a wasteful number, since it uses less digits than its factorization.

21315820 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1065800 (or 1065798 counting only the distinct ones).

The product of its (nonzero) digits is 480, while the sum is 22.

The square root of 21315820 is about 4616.9058903123. The cubic root of 21315820 is about 277.2685947932.

The spelling of 21315820 in words is "twenty-one million, three hundred fifteen thousand, eight hundred twenty".