2171382020721 has 15 divisors (see below), whose sum is σ = 3243689249691. Its totient is φ = 1447579172448.

The previous prime is 2171382020713. The next prime is 2171382020741. The reversal of 2171382020721 is 1270202831712.

It is a happy number.

The square root of 2171382020721 is 1473561.

It is a perfect power (a square), and thus also a powerful number.

2171382020721 is a `hidden beast` number, since 2 + 1 + 71 + 382 + 0 + 207 + 2 + 1 = 666.

It can be written as a sum of positive squares in only one way, i.e., 1118706020721 + 1052676000000 = 1057689^2 + 1026000^2 .

It is not a de Polignac number, because 2171382020721 - 2³ = 2171382020713 is a prime.

It is not an unprimeable number, because it can be changed into a prime (2171382020741) by changing a digit.

It is a polite number, since it can be written in 14 ways as a sum of consecutive naturals, for example, 13180185 + ... + 13343913.

Almost surely, 2^{2171382020721} is an apocalyptic number.

2171382020721 is the 1473561-st square number.

2171382020721 is the 736781-st centered octagonal number.

It is an amenable number.

2171382020721 is a deficient number, since it is larger than the sum of its proper divisors (1072307228970).

2171382020721 is an frugal number, since it uses more digits than its factorization.

2171382020721 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 327470 (or 163732 counting only the distinct ones).

The product of its (nonzero) digits is 18816, while the sum is 36.

Multiplying 2171382020721 by its sum of digits (36), we get a square (78169752745956 = 8841366²).

The spelling of 2171382020721 in words is "two trillion, one hundred seventy-one billion, three hundred eighty-two million, twenty thousand, seven hundred twenty-one".