72128021 has 4 divisors (see below), whose sum is σ = 82432032. Its totient is φ = 61824012.

The previous prime is 72127997. The next prime is 72128051. The reversal of 72128021 is 12082127.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-72128021 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (72128051) 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 3 ways as a sum of consecutive naturals, for example, 5151995 + ... + 5152008.

It is an arithmetic number, because the mean of its divisors is an integer number (20608008).

Almost surely, 2^72128021 is an apocalyptic number.

It is an amenable number.

72128021 is a deficient number, since it is larger than the sum of its proper divisors (10304011).

72128021 is a wasteful number, since it uses less digits than its factorization.

72128021 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 10304010.

The product of its (nonzero) digits is 448, while the sum is 23.

The square root of 72128021 is about 8492.8217336760. The cubic root of 72128021 is about 416.2631875149.

The spelling of 72128021 in words is "seventy-two million, one hundred twenty-eight thousand, twenty-one".