21563220 has 48 divisors (see below), whose sum is σ = 69003648. Its totient is φ = 4928640.

The previous prime is 21563219. The next prime is 21563237. The reversal of 21563220 is 2236512.

It is a Harshad number since it is a multiple of its sum of digits (21).

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, 25251 + ... + 26090.

It is an arithmetic number, because the mean of its divisors is an integer number (1437576).

Almost surely, 2^21563220 is an apocalyptic number.

21563220 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21563220 is an abundant number, since it is smaller than the sum of its proper divisors (47440428).

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

21563220 is a wasteful number, since it uses less digits than its factorization.

21563220 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 51360 (or 51358 counting only the distinct ones).

The product of its (nonzero) digits is 720, while the sum is 21.

The square root of 21563220 is about 4643.6214315984. The cubic root of 21563220 is about 278.3371683250.

Adding to 21563220 its reverse (2236512), we get a palindrome (23799732).

The spelling of 21563220 in words is "twenty-one million, five hundred sixty-three thousand, two hundred twenty".