72121721 has 8 divisors (see below), whose sum is σ = 86008704. Its totient is φ = 59130720.

The previous prime is 72121697. The next prime is 72121757. The reversal of 72121721 is 12712127.

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is not a de Polignac number, because 72121721 - 2²⁶ = 5012857 is a prime.

It is a Harshad number since it is a multiple of its sum of digits (23).

It is a Duffinian number.

It is a Curzon number.

It is not an unprimeable number, because it can be changed into a prime (72120721) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 223820 + ... + 224141.

It is an arithmetic number, because the mean of its divisors is an integer number (10751088).

Almost surely, 2^72121721 is an apocalyptic number.

It is an amenable number.

72121721 is a deficient number, since it is larger than the sum of its proper divisors (13886983).

72121721 is a wasteful number, since it uses less digits than its factorization.

72121721 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 447991.

The product of its digits is 392, while the sum is 23.

The square root of 72121721 is about 8492.4508241143. The cubic root of 72121721 is about 416.2510677016.

Adding to 72121721 its reverse (12712127), we get a palindrome (84833848).

The spelling of 72121721 in words is "seventy-two million, one hundred twenty-one thousand, seven hundred twenty-one".