19661621808 has 90 divisors (see below), whose sum is σ = 52298004276. Its totient is φ = 6365084544.

The previous prime is 19661621803. The next prime is 19661621887. The reversal of 19661621808 is 80812616691.

It is a Harshad number since it is a multiple of its sum of digits (48).

It is not an unprimeable number, because it can be changed into a prime (19661621801) by changing a digit.

It is a polite number, since it can be written in 17 ways as a sum of consecutive naturals, for example, 35944191 + ... + 35944737.

Almost surely, 2^19661621808 is an apocalyptic number.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 19661621808, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (26149002138).

19661621808 is an abundant number, since it is smaller than the sum of its proper divisors (32636382468).

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

19661621808 is an frugal number, since it uses more digits than its factorization.

19661621808 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1179 (or 589 counting only the distinct ones).

The product of its (nonzero) digits is 248832, while the sum is 48.

Multiplying 19661621808 by its sum of digits (48), we get a square (943757846784 = 971472²).

19661621808 divided by its sum of digits (48) gives a square (409617121 = 20239²).

The spelling of 19661621808 in words is "nineteen billion, six hundred sixty-one million, six hundred twenty-one thousand, eight hundred eight".