21005538 has 24 divisors (see below), whose sum is σ = 43421904. Its totient is φ = 6774120.

The previous prime is 21005503. The next prime is 21005539. The reversal of 21005538 is 83550012.

It is not an unprimeable number, because it can be changed into a prime (21005539) by changing a digit.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 3945 + ... + 7587.

It is an arithmetic number, because the mean of its divisors is an integer number (1809246).

Almost surely, 2^21005538 is an apocalyptic number.

21005538 is an abundant number, since it is smaller than the sum of its proper divisors (22416366).

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

21005538 is a wasteful number, since it uses less digits than its factorization.

21005538 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 3710 (or 3679 counting only the distinct ones).

The product of its (nonzero) digits is 1200, while the sum is 24.

The square root of 21005538 is about 4583.1799004621. The cubic root of 21005538 is about 275.9166677638.

The spelling of 21005538 in words is "twenty-one million, five thousand, five hundred thirty-eight".