21538420 has 12 divisors (see below), whose sum is σ = 45230724. Its totient is φ = 8615360.

The previous prime is 21538409. The next prime is 21538421. The reversal of 21538420 is 2483512.

It can be written as a sum of positive squares in 2 ways, for example, as 3526884 + 18011536 = 1878^2 + 4244^2 .

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21538421) 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 3 ways as a sum of consecutive naturals, for example, 538441 + ... + 538480.

It is an arithmetic number, because the mean of its divisors is an integer number (3769227).

Almost surely, 2^21538420 is an apocalyptic number.

21538420 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21538420 is an abundant number, since it is smaller than the sum of its proper divisors (23692304).

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

21538420 is a wasteful number, since it uses less digits than its factorization.

21538420 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1076930 (or 1076928 counting only the distinct ones).

The product of its (nonzero) digits is 1920, while the sum is 25.

The square root of 21538420 is about 4640.9503337140. The cubic root of 21538420 is about 278.2304215934.

The spelling of 21538420 in words is "twenty-one million, five hundred thirty-eight thousand, four hundred twenty".