21821646640 has 20 divisors (see below), whose sum is σ = 50735328624. Its totient is φ = 8728658624.

The previous prime is 21821646619. The next prime is 21821646643. The reversal of 21821646640 is 4664612812.

It is a tau number, because it is divible by the number of its divisors (20).

It is a Harshad number since it is a multiple of its sum of digits (40).

It is a junction number, because it is equal to n+sod(n) for n = 21821646593 and 21821646602.

It is not an unprimeable number, because it can be changed into a prime (21821646643) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 136385212 + ... + 136385371.

Almost surely, 2^21821646640 is an apocalyptic number.

21821646640 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21821646640 is an abundant number, since it is smaller than the sum of its proper divisors (28913681984).

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

21821646640 is a wasteful number, since it uses less digits than its factorization.

21821646640 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 272770596 (or 272770590 counting only the distinct ones).

The product of its (nonzero) digits is 110592, while the sum is 40.

The spelling of 21821646640 in words is "twenty-one billion, eight hundred twenty-one million, six hundred forty-six thousand, six hundred forty".