21312820 has 24 divisors (see below), whose sum is σ = 44922024. Its totient is φ = 8493696.

The previous prime is 21312793. The next prime is 21312829. The reversal of 21312820 is 2821312.

It can be written as a sum of positive squares in 4 ways, for example, as 1705636 + 19607184 = 1306^2 + 4428^2 .

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21312829) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 4042 + ... + 7678.

It is an arithmetic number, because the mean of its divisors is an integer number (1871751).

Almost surely, 2^21312820 is an apocalyptic number.

21312820 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21312820 is an abundant number, since it is smaller than the sum of its proper divisors (23609204).

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

21312820 is a wasteful number, since it uses less digits than its factorization.

21312820 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 3939 (or 3937 counting only the distinct ones).

The product of its (nonzero) digits is 192, while the sum is 19.

The square root of 21312820 is about 4616.5809859679. The cubic root of 21312820 is about 277.2555865390.

The spelling of 21312820 in words is "twenty-one million, three hundred twelve thousand, eight hundred twenty".