21216557 has 16 divisors (see below), whose sum is σ = 22982400. Its totient is φ = 19536000.

The previous prime is 21216553. The next prime is 21216607. The reversal of 21216557 is 75561212.

It is a cyclic number.

It is not a de Polignac number, because 21216557 - 2² = 21216553 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21216551) 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, 140432 + ... + 140582.

It is an arithmetic number, because the mean of its divisors is an integer number (1436400).

Almost surely, 2^21216557 is an apocalyptic number.

It is an amenable number.

21216557 is a deficient number, since it is larger than the sum of its proper divisors (1765843).

21216557 is a wasteful number, since it uses less digits than its factorization.

21216557 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 364.

The product of its digits is 4200, while the sum is 29.

The square root of 21216557 is about 4606.1433976810. The cubic root of 21216557 is about 276.8375323952.

Adding to 21216557 its reverse (75561212), we get a palindrome (96777769).

The spelling of 21216557 in words is "twenty-one million, two hundred sixteen thousand, five hundred fifty-seven".