18721220 has 24 divisors (see below), whose sum is σ = 44931264. Its totient is φ = 6418656.

The previous prime is 18721217. The next prime is 18721229. The reversal of 18721220 is 2212781.

It is not an unprimeable number, because it can be changed into a prime (18721229) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 66722 + ... + 67001.

It is an arithmetic number, because the mean of its divisors is an integer number (1872136).

Almost surely, 2^18721220 is an apocalyptic number.

18721220 is a gapful number since it is divisible by the number (10) formed by its first and last digit.

It is an amenable number.

18721220 is an abundant number, since it is smaller than the sum of its proper divisors (26210044).

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

18721220 is a wasteful number, since it uses less digits than its factorization.

18721220 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 133739 (or 133737 counting only the distinct ones).

The product of its (nonzero) digits is 448, while the sum is 23.

The square root of 18721220 is about 4326.8025145597. The cubic root of 18721220 is about 265.5286468523.

The spelling of 18721220 in words is "eighteen million, seven hundred twenty-one thousand, two hundred twenty".