21618821 has 16 divisors (see below), whose sum is σ = 25229568. Its totient is φ = 18144000.

The previous prime is 21618803. The next prime is 21618847. The reversal of 21618821 is 12881612.

It is a de Polignac number, because none of the positive numbers 2^k-21618821 is a prime.

It is a Smith number, since the sum of its digits (29) coincides with the sum of the digits of its prime factors. Since it is squarefree, it is also a hoax number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21618221) 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, 119351 + ... + 119531.

It is an arithmetic number, because the mean of its divisors is an integer number (1576848).

Almost surely, 2^21618821 is an apocalyptic number.

It is an amenable number.

21618821 is a deficient number, since it is larger than the sum of its proper divisors (3610747).

21618821 is a wasteful number, since it uses less digits than its factorization.

21618821 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 452.

The product of its digits is 1536, while the sum is 29.

The square root of 21618821 is about 4649.6043917736. The cubic root of 21618821 is about 278.5761948153.

The spelling of 21618821 in words is "twenty-one million, six hundred eighteen thousand, eight hundred twenty-one".