19805949891 has 72 divisors (see below), whose sum is σ = 36808362864. Its totient is φ = 10164631680.

The previous prime is 19805949869. The next prime is 19805949893. The reversal of 19805949891 is 19894950891.

19805949891 is a `hidden beast` number, since 1 + 9 + 8 + 0 + 59 + 498 + 91 = 666.

It is not a de Polignac number, because 19805949891 - 2⁷ = 19805949763 is a prime.

It is a Harshad number since it is a multiple of its sum of digits (63).

It is not an unprimeable number, because it can be changed into a prime (19805949893) by changing a digit.

It is a polite number, since it can be written in 71 ways as a sum of consecutive naturals, for example, 165436 + ... + 258806.

It is an arithmetic number, because the mean of its divisors is an integer number (511227262).

Almost surely, 2^19805949891 is an apocalyptic number.

19805949891 is a deficient number, since it is larger than the sum of its proper divisors (17002412973).

19805949891 is a wasteful number, since it uses less digits than its factorization.

19805949891 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 93441 (or 93431 counting only the distinct ones).

The product of its (nonzero) digits is 8398080, while the sum is 63.

The spelling of 19805949891 in words is "nineteen billion, eight hundred five million, nine hundred forty-nine thousand, eight hundred ninety-one".