21055540656 has 80 divisors (see below), whose sum is σ = 55464735744. Its totient is φ = 6880503552.

The previous prime is 21055540651. The next prime is 21055540657. The reversal of 21055540656 is 65604555012.

It is a happy number.

It is not an unprimeable number, because it can be changed into a prime (21055540651) 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, 4136545 + ... + 4141631.

Almost surely, 2^21055540656 is an apocalyptic number.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21055540656, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (27732367872).

21055540656 is an abundant number, since it is smaller than the sum of its proper divisors (34409195088).

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

21055540656 is a wasteful number, since it uses less digits than its factorization.

21055540656 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 6778 (or 6772 counting only the distinct ones).

The product of its (nonzero) digits is 180000, while the sum is 39.

The spelling of 21055540656 in words is "twenty-one billion, fifty-five million, five hundred forty thousand, six hundred fifty-six".