21221816 has 64 divisors (see below), whose sum is σ = 50734080. Its totient is φ = 8081280.

The previous prime is 21221791. The next prime is 21221821. The reversal of 21221816 is 61812212.

It is a junction number, because it is equal to n+sod(n) for n = 21221791 and 21221800.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 28586 + ... + 29318.

It is an arithmetic number, because the mean of its divisors is an integer number (792720).

Almost surely, 2^21221816 is an apocalyptic number.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21221816, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (25367040).

21221816 is an abundant number, since it is smaller than the sum of its proper divisors (29512264).

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

21221816 is a wasteful number, since it uses less digits than its factorization.

21221816 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 804 (or 800 counting only the distinct ones).

The product of its digits is 384, while the sum is 23.

The square root of 21221816 is about 4606.7142303381. The cubic root of 21221816 is about 276.8604039715.

The spelling of 21221816 in words is "twenty-one million, two hundred twenty-one thousand, eight hundred sixteen".