18836721 has 12 divisors (see below), whose sum is σ = 27490372. Its totient is φ = 12427776.

The previous prime is 18836717. The next prime is 18836723. The reversal of 18836721 is 12763881.

It can be written as a sum of positive squares in 2 ways, for example, as 12531600 + 6305121 = 3540^2 + 2511^2 .

It is not a de Polignac number, because 18836721 - 2² = 18836717 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (18836723) by changing a digit.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 9916 + ... + 11661.

Almost surely, 2^18836721 is an apocalyptic number.

It is an amenable number.

18836721 is a deficient number, since it is larger than the sum of its proper divisors (8653651).

18836721 is a wasteful number, since it uses less digits than its factorization.

18836721 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 21680 (or 21677 counting only the distinct ones).

The product of its digits is 16128, while the sum is 36.

The square root of 18836721 is about 4340.1291455439. The cubic root of 18836721 is about 266.0735894158.

The spelling of 18836721 in words is "eighteen million, eight hundred thirty-six thousand, seven hundred twenty-one".