21557205640 has 64 divisors (see below), whose sum is σ = 51396813360. Its totient is φ = 8109342720.

The previous prime is 21557205629. The next prime is 21557205643. The reversal of 21557205640 is 4650275512.

It can be written as a sum of positive squares in 8 ways, for example, as 2926593604 + 18630612036 = 54098^2 + 136494^2 .

It is a self number, because there is not a number n which added to its sum of digits gives 21557205640.

It is not an unprimeable number, because it can be changed into a prime (21557205643) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 913834 + ... + 937126.

Almost surely, 2^21557205640 is an apocalyptic number.

21557205640 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 21557205640, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (25698406680).

21557205640 is an abundant number, since it is smaller than the sum of its proper divisors (29839607720).

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

21557205640 is a wasteful number, since it uses less digits than its factorization.

21557205640 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 24682 (or 24678 counting only the distinct ones).

The product of its (nonzero) digits is 84000, while the sum is 37.

The spelling of 21557205640 in words is "twenty-one billion, five hundred fifty-seven million, two hundred five thousand, six hundred forty".