19781813520 has 720 divisors, whose sum is σ = 84437720640. Its totient is φ = 4279661568.

The previous prime is 19781813489. The next prime is 19781813521. The reversal of 19781813520 is 2531818791.

It is a tau number, because it is divible by the number of its divisors (720).

It is a super-2 number, since 2×19781813520² (a number of 21 digits) contains 22 as substring.

It is a Harshad number since it is a multiple of its sum of digits (45).

It is not an unprimeable number, because it can be changed into a prime (19781813521) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 143 ways as a sum of consecutive naturals, for example, 18098094 + ... + 18099186.

It is an arithmetic number, because the mean of its divisors is an integer number (117274612).

Almost surely, 2^19781813520 is an apocalyptic number.

19781813520 is a gapful number since it is divisible by the number (10) formed by its first and last digit.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 19781813520, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (42218860320).

19781813520 is an abundant number, since it is smaller than the sum of its proper divisors (64655907120).

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

19781813520 is a wasteful number, since it uses less digits than its factorization.

19781813520 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1154 (or 1129 counting only the distinct ones).

The product of its (nonzero) digits is 120960, while the sum is 45.

The spelling of 19781813520 in words is "nineteen billion, seven hundred eighty-one million, eight hundred thirteen thousand, five hundred twenty".