21643220 has 12 divisors (see below), whose sum is σ = 45450804. Its totient is φ = 8657280.

The previous prime is 21643217. The next prime is 21643231. The reversal of 21643220 is 2234612.

It can be written as a sum of positive squares in 2 ways, for example, as 7997584 + 13645636 = 2828^2 + 3694^2 .

It is a Harshad number since it is a multiple of its sum of digits (20), and also a Moran number because the ratio is a prime number: 1082161 = 21643220 / (2 + 1 + 6 + 4 + 3 + 2 + 2 + 0).

It is a junction number, because it is equal to n+sod(n) for n = 21643192 and 21643201.

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, 541061 + ... + 541100.

It is an arithmetic number, because the mean of its divisors is an integer number (3787567).

Almost surely, 2^21643220 is an apocalyptic number.

21643220 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21643220 is an abundant number, since it is smaller than the sum of its proper divisors (23807584).

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

21643220 is a wasteful number, since it uses less digits than its factorization.

21643220 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1082170 (or 1082168 counting only the distinct ones).

The product of its (nonzero) digits is 576, while the sum is 20.

The square root of 21643220 is about 4652.2274235037. The cubic root of 21643220 is about 278.6809557727.

Adding to 21643220 its reverse (2234612), we get a palindrome (23877832).

The spelling of 21643220 in words is "twenty-one million, six hundred forty-three thousand, two hundred twenty".