19721391956 has 24 divisors (see below), whose sum is σ = 39918002880. Its totient is φ = 8350192512.

The previous prime is 19721391947. The next prime is 19721391961. The reversal of 19721391956 is 65919312791.

It is a junction number, because it is equal to n+sod(n) for n = 19721391898 and 19721391907.

It is a congruent number.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (19) of ones.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 4240661 + ... + 4245308.

It is an arithmetic number, because the mean of its divisors is an integer number (1663250120).

Almost surely, 2^19721391956 is an apocalyptic number.

It is an amenable number.

19721391956 is an abundant number, since it is smaller than the sum of its proper divisors (20196610924).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

19721391956 is a wasteful number, since it uses less digits than its factorization.

19721391956 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 8486063 (or 8486061 counting only the distinct ones).

The product of its digits is 918540, while the sum is 53.

The spelling of 19721391956 in words is "nineteen billion, seven hundred twenty-one million, three hundred ninety-one thousand, nine hundred fifty-six".