21988521 has 12 divisors (see below), whose sum is σ = 31914480. Its totient is φ = 14588280.

The previous prime is 21988513. The next prime is 21988541. The reversal of 21988521 is 12588912.

It is not a de Polignac number, because 21988521 - 2³ = 21988513 is a prime.

It is not an unprimeable number, because it can be changed into a prime (21988511) 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, 3891 + ... + 7688.

It is an arithmetic number, because the mean of its divisors is an integer number (2659540).

Almost surely, 2^21988521 is an apocalyptic number.

It is an amenable number.

21988521 is a deficient number, since it is larger than the sum of its proper divisors (9925959).

21988521 is a wasteful number, since it uses less digits than its factorization.

21988521 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 11796 (or 11793 counting only the distinct ones).

The product of its digits is 11520, while the sum is 36.

The square root of 21988521 is about 4689.1919346514. The cubic root of 21988521 is about 280.1551903302.

The spelling of 21988521 in words is "twenty-one million, nine hundred eighty-eight thousand, five hundred twenty-one".