18444627721 has 27 divisors (see below), whose sum is σ = 20699066133. Its totient is φ = 16427698560.

The previous prime is 18444627671. The next prime is 18444627737. The reversal of 18444627721 is 12772644481.

The square root of 18444627721 is 135811.

It is a perfect power (a square), and thus also a powerful number.

It can be written as a sum of positive squares in 4 ways, for example, as 6401760121 + 12042867600 = 80011^2 + 109740^2 .

It is not a de Polignac number, because 18444627721 - 2⁹ = 18444627209 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (18444624721) by changing a digit.

It is a polite number, since it can be written in 26 ways as a sum of consecutive naturals, for example, 54731665 + ... + 54732001.

It is an arithmetic number, because the mean of its divisors is an integer number (766632079).

Almost surely, 2^18444627721 is an apocalyptic number.

18444627721 is the 135811-st square number.

18444627721 is the 67906-th centered octagonal number.

It is an amenable number.

18444627721 is a deficient number, since it is larger than the sum of its proper divisors (2254438412).

18444627721 is an frugal number, since it uses more digits than its factorization.

18444627721 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 762 (or 381 counting only the distinct ones).

The product of its digits is 602112, while the sum is 46.

The spelling of 18444627721 in words is "eighteen billion, four hundred forty-four million, six hundred twenty-seven thousand, seven hundred twenty-one".