2166021571081 has 9 divisors (see below), whose sum is σ = 2300956067221. Its totient is φ = 2038584989632.

The previous prime is 2166021571079. The next prime is 2166021571117. The reversal of 2166021571081 is 1801751206612.

The square root of 2166021571081 is 1471741.

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

It can be written as a sum of positive squares in 4 ways, for example, as 66594447481 + 2099427123600 = 258059^2 + 1448940^2 .

It is not a de Polignac number, because 2166021571081 - 2¹ = 2166021571079 is a prime.

It is a super-2 number, since 2×2166021571081² (a number of 25 digits) contains 22 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (2166021571981) 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 8 ways as a sum of consecutive naturals, for example, 24976311 + ... + 25062883.

Almost surely, 2^{2166021571081} is an apocalyptic number.

2166021571081 is the 1471741-st square number.

2166021571081 is the 735871-st centered octagonal number.

It is an amenable number.

2166021571081 is a deficient number, since it is larger than the sum of its proper divisors (134934496140).

2166021571081 is an frugal number, since it uses more digits than its factorization.

2166021571081 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 173180 (or 86590 counting only the distinct ones).

The product of its (nonzero) digits is 40320, while the sum is 40.

Adding to 2166021571081 its reverse (1801751206612), we get a palindrome (3967772777693).

The spelling of 2166021571081 in words is "two trillion, one hundred sixty-six billion, twenty-one million, five hundred seventy-one thousand, eighty-one".