21640489920 has 504 divisors, whose sum is σ = 87979069152. Its totient is φ = 4782551040.

The previous prime is 21640489903. The next prime is 21640489957. The reversal of 21640489920 is 2998404612.

21640489920 is a `hidden beast` number, since 2 + 164 + 0 + 489 + 9 + 2 + 0 = 666.

It is a tau number, because it is divible by the number of its divisors (504).

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

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 71 ways as a sum of consecutive naturals, for example, 19373202 + ... + 19374318.

Almost surely, 2^21640489920 is an apocalyptic number.

21640489920 is a gapful number since it is divisible by the number (20) 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 21640489920, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (43989534576).

21640489920 is an abundant number, since it is smaller than the sum of its proper divisors (66338579232).

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

21640489920 is a wasteful number, since it uses less digits than its factorization.

21640489920 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1209 (or 1165 counting only the distinct ones).

The product of its (nonzero) digits is 248832, while the sum is 45.

The spelling of 21640489920 in words is "twenty-one billion, six hundred forty million, four hundred eighty-nine thousand, nine hundred twenty".