19956497891 has 32 divisors (see below), whose sum is σ = 22534848000. Its totient is φ = 17515872000.

The previous prime is 19956497851. The next prime is 19956497903. The reversal of 19956497891 is 19879465991.

It is not a de Polignac number, because 19956497891 - 2²⁶ = 19889389027 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (19956497801) by changing a digit.

It is a polite number, since it can be written in 31 ways as a sum of consecutive naturals, for example, 20552036 + ... + 20553006.

It is an arithmetic number, because the mean of its divisors is an integer number (704214000).

Almost surely, 2^19956497891 is an apocalyptic number.

19956497891 is a gapful number since it is divisible by the number (11) formed by its first and last digit.

19956497891 is a deficient number, since it is larger than the sum of its proper divisors (2578350109).

19956497891 is a wasteful number, since it uses less digits than its factorization.

19956497891 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1451.

The product of its digits is 44089920, while the sum is 68.

The spelling of 19956497891 in words is "nineteen billion, nine hundred fifty-six million, four hundred ninety-seven thousand, eight hundred ninety-one".