21321816 has 16 divisors (see below), whose sum is σ = 53304600. Its totient is φ = 7107264.

The previous prime is 21321809. The next prime is 21321821. The reversal of 21321816 is 61812312.

It is a Harshad number since it is a multiple of its sum of digits (24), and also a Moran number because the ratio is a prime number: 888409 = 21321816 / (2 + 1 + 3 + 2 + 1 + 8 + 1 + 6).

It is a nude number because it is divisible by every one of its digits.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 444181 + ... + 444228.

Almost surely, 2^21321816 is an apocalyptic number.

It is an amenable number.

21321816 is an abundant number, since it is smaller than the sum of its proper divisors (31982784).

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

21321816 is a wasteful number, since it uses less digits than its factorization.

21321816 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 888418 (or 888414 counting only the distinct ones).

The product of its digits is 576, while the sum is 24.

The square root of 21321816 is about 4617.5551972878. Note that the first 3 decimals coincide. The cubic root of 21321816 is about 277.2945903000.

The spelling of 21321816 in words is "twenty-one million, three hundred twenty-one thousand, eight hundred sixteen".