21640638240 has 768 divisors, whose sum is σ = 90988531200. Its totient is φ = 4745723904.

The previous prime is 21640638233. The next prime is 21640638241. The reversal of 21640638240 is 4283604612.

21640638240 is a `hidden beast` number, since 2 + 1 + 6 + 406 + 3 + 8 + 240 = 666.

It is a Harshad number since it is a multiple of its sum of digits (36).

It is a junction number, because it is equal to n+sod(n) for n = 21640638195 and 21640638204.

It is not an unprimeable number, because it can be changed into a prime (21640638241) by changing a digit.

It is a polite number, since it can be written in 127 ways as a sum of consecutive naturals, for example, 18139084 + ... + 18140276.

It is an arithmetic number, because the mean of its divisors is an integer number (118474650).

Almost surely, 2^21640638240 is an apocalyptic number.

21640638240 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 21640638240, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (45494265600).

21640638240 is an abundant number, since it is smaller than the sum of its proper divisors (69347892960).

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

21640638240 is a wasteful number, since it uses less digits than its factorization.

21640638240 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1266 (or 1252 counting only the distinct ones).

The product of its (nonzero) digits is 55296, while the sum is 36.

The spelling of 21640638240 in words is "twenty-one billion, six hundred forty million, six hundred thirty-eight thousand, two hundred forty".