215328721 has 4 divisors (see below), whose sum is σ = 215532352. Its totient is φ = 215125092.

The previous prime is 215328703. The next prime is 215328733. The reversal of 215328721 is 127823512.

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 not a de Polignac number, because 215328721 - 2⁵ = 215328689 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (215328781) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 100221 + ... + 102346.

It is an arithmetic number, because the mean of its divisors is an integer number (53883088).

Almost surely, 2^215328721 is an apocalyptic number.

It is an amenable number.

215328721 is a deficient number, since it is larger than the sum of its proper divisors (203631).

215328721 is a wasteful number, since it uses less digits than its factorization.

215328721 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 203630.

The product of its digits is 6720, while the sum is 31.

The square root of 215328721 is about 14674.0833103809. The cubic root of 215328721 is about 599.3778003728.

The spelling of 215328721 in words is "two hundred fifteen million, three hundred twenty-eight thousand, seven hundred twenty-one".