1891947981361 has 3 divisors (see below), whose sum is σ = 1891949356843. Its totient is φ = 1891946605880.

The previous prime is 1891947981353. The next prime is 1891947981403. The reversal of 1891947981361 is 1631897491981.

The square root of 1891947981361 is 1375481.

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

It is a semiprime because it is the product of two primes, and also a brilliant number, because the two primes have the same length.

It can be written as a sum of positive squares in only one way, i.e., 156405221361 + 1735542760000 = 395481^2 + 1317400^2 .

It is not a de Polignac number, because 1891947981361 - 2³ = 1891947981353 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (1891947981311) 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 2 ways as a sum of consecutive naturals, for example, 687741 + ... + 2063221.

Almost surely, 2^{1891947981361} is an apocalyptic number.

1891947981361 is the 1375481-st square number.

1891947981361 is the 687741-st centered octagonal number.

It is an amenable number.

1891947981361 is a deficient number, since it is larger than the sum of its proper divisors (1375482).

1891947981361 is an frugal number, since it uses more digits than its factorization.

1891947981361 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2750962 (or 1375481 counting only the distinct ones).

The product of its digits is 23514624, while the sum is 67.

The spelling of 1891947981361 in words is "one trillion, eight hundred ninety-one billion, nine hundred forty-seven million, nine hundred eighty-one thousand, three hundred sixty-one".