21801220 has 24 divisors (see below), whose sum is σ = 52323264. Its totient is φ = 7474656.

The previous prime is 21801211. The next prime is 21801271. The reversal of 21801220 is 2210812.

It is a junction number, because it is equal to n+sod(n) for n = 21801194 and 21801203.

It is an unprimeable number.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 77722 + ... + 78001.

It is an arithmetic number, because the mean of its divisors is an integer number (2180136).

Almost surely, 2^21801220 is an apocalyptic number.

21801220 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21801220 is an abundant number, since it is smaller than the sum of its proper divisors (30522044).

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

21801220 is a wasteful number, since it uses less digits than its factorization.

21801220 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 155739 (or 155737 counting only the distinct ones).

The product of its (nonzero) digits is 64, while the sum is 16.

The square root of 21801220 is about 4669.1776577894. The cubic root of 21801220 is about 279.3574551856.

The spelling of 21801220 in words is "twenty-one million, eight hundred one thousand, two hundred twenty".