72817921 has 6 divisors (see below), whose sum is σ = 80039666. Its totient is φ = 66198000.

The previous prime is 72817903. The next prime is 72817933. The reversal of 72817921 is 12971827.

It can be written as a sum of positive squares in only one way, i.e., 63600625 + 9217296 = 7975^2 + 3036^2 .

It is a de Polignac number, because none of the positive numbers 2^k-72817921 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (72817981) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 300780 + ... + 301021.

Almost surely, 2^72817921 is an apocalyptic number.

It is an amenable number.

72817921 is a deficient number, since it is larger than the sum of its proper divisors (7221745).

72817921 is a wasteful number, since it uses less digits than its factorization.

72817921 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 601823 (or 601812 counting only the distinct ones).

The product of its digits is 14112, while the sum is 37.

The square root of 72817921 is about 8533.3417252563. The cubic root of 72817921 is about 417.5861555019.

The spelling of 72817921 in words is "seventy-two million, eight hundred seventeen thousand, nine hundred twenty-one".