19921904640 has 660 divisors, whose sum is σ = 78666381948. Its totient is φ = 4817387520.

The previous prime is 19921904623. The next prime is 19921904689. The reversal of 19921904640 is 4640912991.

19921904640 is a `hidden beast` number, since 19 + 92 + 1 + 90 + 464 + 0 = 666.

It can be written as a sum of positive squares in 2 ways, for example, as 10277093376 + 9644811264 = 101376^2 + 98208^2 .

It is a tau number, because it is divible by the number of its divisors (660).

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

It is an unprimeable number.

It is a polite number, since it can be written in 59 ways as a sum of consecutive naturals, for example, 50180922 + ... + 50181318.

Almost surely, 2^19921904640 is an apocalyptic number.

19921904640 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 19921904640, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (39333190974).

19921904640 is an abundant number, since it is smaller than the sum of its proper divisors (58744477308).

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

19921904640 is a wasteful number, since it uses less digits than its factorization.

19921904640 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 456 (or 418 counting only the distinct ones).

The product of its (nonzero) digits is 139968, while the sum is 45.

The spelling of 19921904640 in words is "nineteen billion, nine hundred twenty-one million, nine hundred four thousand, six hundred forty".