21287538 has 24 divisors (see below), whose sum is σ = 46208448. Its totient is φ = 7082712.

The previous prime is 21287531. The next prime is 21287551. The reversal of 21287538 is 83578212.

It is not an unprimeable number, because it can be changed into a prime (21287531) 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 11 ways as a sum of consecutive naturals, for example, 16795 + ... + 18017.

It is an arithmetic number, because the mean of its divisors is an integer number (1925352).

Almost surely, 2^21287538 is an apocalyptic number.

21287538 is an abundant number, since it is smaller than the sum of its proper divisors (24920910).

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

21287538 is a wasteful number, since it uses less digits than its factorization.

21287538 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2198 (or 2195 counting only the distinct ones).

The product of its digits is 26880, while the sum is 36.

The square root of 21287538 is about 4613.8419998955. The cubic root of 21287538 is about 277.1459131244.

The spelling of 21287538 in words is "twenty-one million, two hundred eighty-seven thousand, five hundred thirty-eight".