19939981681 has 3 divisors (see below), whose sum is σ = 19940122891. Its totient is φ = 19939840472.

The previous prime is 19939981679. The next prime is 19939981693. The reversal of 19939981681 is 18618993991.

The square root of 19939981681 is 141209.

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., 4043815281 + 15896166400 = 63591^2 + 126080^2 .

It is not a de Polignac number, because 19939981681 - 2¹ = 19939981679 is a prime.

It is a super-3 number, since 3×19939981681³ (a number of 32 digits) contains 333 as substring. Note that it is a super-d number also for d = 2.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (19939981081) 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, 70605 + ... + 211813.

Almost surely, 2^19939981681 is an apocalyptic number.

19939981681 is the 141209-th square number.

19939981681 is the 70605-th centered octagonal number.

It is an amenable number.

19939981681 is a deficient number, since it is larger than the sum of its proper divisors (141210).

19939981681 is an frugal number, since it uses more digits than its factorization.

19939981681 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 282418 (or 141209 counting only the distinct ones).

The product of its digits is 7558272, while the sum is 64.

Multiplying 19939981681 by its sum of digits (64), we get a square (1276158827584 = 1129672²).

The spelling of 19939981681 in words is "nineteen billion, nine hundred thirty-nine million, nine hundred eighty-one thousand, six hundred eighty-one".