72005818921 has 27 divisors (see below), whose sum is σ = 75522673317. Its totient is φ = 68651849760.

The previous prime is 72005818891. The next prime is 72005818939. The reversal of 72005818921 is 12981850027.

It is a happy number.

The square root of 72005818921 is 268339.

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 9673706025 + 62332112896 = 98355^2 + 249664^2 .

It is not a de Polignac number, because 72005818921 - 2⁵ = 72005818889 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (72005818991) 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, 867539946 + ... + 867540028.

Almost surely, 2^72005818921 is an apocalyptic number.

72005818921 is the 268339-th square number.

72005818921 is the 134170-th centered octagonal number.

It is an amenable number.

72005818921 is a deficient number, since it is larger than the sum of its proper divisors (3516854396).

72005818921 is an frugal number, since it uses more digits than its factorization.

72005818921 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 394 (or 197 counting only the distinct ones).

The product of its (nonzero) digits is 80640, while the sum is 43.

The spelling of 72005818921 in words is "seventy-two billion, five million, eight hundred eighteen thousand, nine hundred twenty-one".