21208813640 has 32 divisors (see below), whose sum is σ = 54536950080. Its totient is φ = 7271593152.

The previous prime is 21208813601. The next prime is 21208813643. The reversal of 21208813640 is 4631880212.

It is a Harshad number since it is a multiple of its sum of digits (35).

It is a self number, because there is not a number n which added to its sum of digits gives 21208813640.

It is not an unprimeable number, because it can be changed into a prime (21208813643) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 37872602 + ... + 37873161.

It is an arithmetic number, because the mean of its divisors is an integer number (1704279690).

Almost surely, 2^21208813640 is an apocalyptic number.

21208813640 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21208813640 is an abundant number, since it is smaller than the sum of its proper divisors (33328136440).

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

21208813640 is a wasteful number, since it uses less digits than its factorization.

21208813640 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 75745781 (or 75745777 counting only the distinct ones).

The product of its (nonzero) digits is 18432, while the sum is 35.

The spelling of 21208813640 in words is "twenty-one billion, two hundred eight million, eight hundred thirteen thousand, six hundred forty".