18444721 has 16 divisors (see below), whose sum is σ = 19819008. Its totient is φ = 17136000.

The previous prime is 18444707. The next prime is 18444731. The reversal of 18444721 is 12744481.

It is a happy number.

It is a cyclic number.

It is not a de Polignac number, because 18444721 - 2¹³ = 18436529 is a prime.

It is a Harshad number since it is a multiple of its sum of digits (31).

It is a deceptive number, since it divides R_18444720.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (18444731) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 134565 + ... + 134701.

It is an arithmetic number, because the mean of its divisors is an integer number (1238688).

Almost surely, 2^18444721 is an apocalyptic number.

It is an amenable number.

18444721 is a deficient number, since it is larger than the sum of its proper divisors (1374287).

18444721 is a wasteful number, since it uses less digits than its factorization.

18444721 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 312.

The product of its digits is 7168, while the sum is 31.

The square root of 18444721 is about 4294.7317727653. The cubic root of 18444721 is about 264.2149353472.

The spelling of 18444721 in words is "eighteen million, four hundred forty-four thousand, seven hundred twenty-one".