21638020 has 12 divisors (see below), whose sum is σ = 45439884. Its totient is φ = 8655200.

The previous prime is 21637997. The next prime is 21638033. The reversal of 21638020 is 2083612.

It can be written as a sum of positive squares in 2 ways, for example, as 10023556 + 11614464 = 3166^2 + 3408^2 .

It is a junction number, because it is equal to n+sod(n) for n = 21637982 and 21638000.

It is an unprimeable number.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 540931 + ... + 540970.

It is an arithmetic number, because the mean of its divisors is an integer number (3786657).

Almost surely, 2^21638020 is an apocalyptic number.

21638020 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21638020 is an abundant number, since it is smaller than the sum of its proper divisors (23801864).

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

21638020 is a wasteful number, since it uses less digits than its factorization.

21638020 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1081910 (or 1081908 counting only the distinct ones).

The product of its (nonzero) digits is 576, while the sum is 22.

The square root of 21638020 is about 4651.6685178546. The cubic root of 21638020 is about 278.6586353563.

The spelling of 21638020 in words is "twenty-one million, six hundred thirty-eight thousand, twenty".