72172921 has 4 divisors (see below), whose sum is σ = 72234612. Its totient is φ = 72111232.

The previous prime is 72172897. The next prime is 72172951. The reversal of 72172921 is 12927127.

It is a happy number.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 54834025 + 17338896 = 7405^2 + 4164^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-72172921 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (72172951) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 29056 + ... + 31441.

It is an arithmetic number, because the mean of its divisors is an integer number (18058653).

Almost surely, 2^72172921 is an apocalyptic number.

It is an amenable number.

72172921 is a deficient number, since it is larger than the sum of its proper divisors (61691).

72172921 is a wasteful number, since it uses less digits than its factorization.

72172921 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 61690.

The product of its digits is 3528, while the sum is 31.

The square root of 72172921 is about 8495.4647312551. The cubic root of 72172921 is about 416.3495447999.

The spelling of 72172921 in words is "seventy-two million, one hundred seventy-two thousand, nine hundred twenty-one".