21228537 has 16 divisors (see below), whose sum is σ = 31537152. Its totient is φ = 12591120.

The previous prime is 21228533. The next prime is 21228553. The reversal of 21228537 is 73582212.

It is not a de Polignac number, because 21228537 - 2² = 21228533 is a prime.

It is not an unprimeable number, because it can be changed into a prime (21228533) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 5293 + ... + 8394.

It is an arithmetic number, because the mean of its divisors is an integer number (1971072).

Almost surely, 2^21228537 is an apocalyptic number.

It is an amenable number.

21228537 is a deficient number, since it is larger than the sum of its proper divisors (10308615).

21228537 is a wasteful number, since it uses less digits than its factorization.

21228537 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 13748.

The product of its digits is 6720, while the sum is 30.

The square root of 21228537 is about 4607.4436513103. The cubic root of 21228537 is about 276.8896283378.

The spelling of 21228537 in words is "twenty-one million, two hundred twenty-eight thousand, five hundred thirty-seven".