18640721 has 16 divisors (see below), whose sum is σ = 21809088. Its totient is φ = 15744000.

The previous prime is 18640693. The next prime is 18640723. The reversal of 18640721 is 12704681.

It is a cyclic number.

It is not a de Polignac number, because 18640721 - 2²² = 14446417 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (18640723) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 14921 + ... + 16121.

It is an arithmetic number, because the mean of its divisors is an integer number (1363068).

Almost surely, 2^18640721 is an apocalyptic number.

18640721 is a gapful number since it is divisible by the number (11) formed by its first and last digit.

It is an amenable number.

18640721 is a deficient number, since it is larger than the sum of its proper divisors (3168367).

18640721 is a wasteful number, since it uses less digits than its factorization.

18640721 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1312.

The product of its (nonzero) digits is 2688, while the sum is 29.

The square root of 18640721 is about 4317.4901273772. The cubic root of 18640721 is about 265.1475196201.

The spelling of 18640721 in words is "eighteen million, six hundred forty thousand, seven hundred twenty-one".