21538428 has 24 divisors (see below), whose sum is σ = 51878400. Its totient is φ = 6947760.

The previous prime is 21538427. The next prime is 21538453. The reversal of 21538428 is 82483512.

It is a super-2 number, since 2×21538428² = 927807761422368, which contains 22 as substring.

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 polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 28578 + ... + 29321.

It is an arithmetic number, because the mean of its divisors is an integer number (2161600).

Almost surely, 2^21538428 is an apocalyptic number.

It is an amenable number.

21538428 is an abundant number, since it is smaller than the sum of its proper divisors (30339972).

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

21538428 is a wasteful number, since it uses less digits than its factorization.

21538428 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 57937 (or 57935 counting only the distinct ones).

The product of its digits is 15360, while the sum is 33.

The square root of 21538428 is about 4640.9511956063. The cubic root of 21538428 is about 278.2304560411.

It can be divided in two parts, 2153842 and 8, that added together give a triangular number (2153850 = T₂₀₇₅).

The spelling of 21538428 in words is "twenty-one million, five hundred thirty-eight thousand, four hundred twenty-eight".