2171530721 has 4 divisors (see below), whose sum is σ = 2174077332. Its totient is φ = 2168984112.

The previous prime is 2171530679. The next prime is 2171530733. The reversal of 2171530721 is 1270351712.

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 562638400 + 1608892321 = 23720^2 + 40111^2 .

It is a cyclic number.

It is not a de Polignac number, because 2171530721 - 2⁶ = 2171530657 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (2171530771) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 1272026 + ... + 1273731.

It is an arithmetic number, because the mean of its divisors is an integer number (543519333).

Almost surely, 2^2171530721 is an apocalyptic number.

It is an amenable number.

2171530721 is a deficient number, since it is larger than the sum of its proper divisors (2546611).

2171530721 is an equidigital number, since it uses as much as digits as its factorization.

2171530721 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2546610.

The product of its (nonzero) digits is 2940, while the sum is 29.

The square root of 2171530721 is about 46599.6858465806. The cubic root of 2171530721 is about 1294.9569354055.

The spelling of 2171530721 in words is "two billion, one hundred seventy-one million, five hundred thirty thousand, seven hundred twenty-one".