21355120540 has 72 divisors (see below), whose sum is σ = 49873531680. Its totient is φ = 7671815424.

The previous prime is 21355120517. The next prime is 21355120541. The reversal of 21355120540 is 4502155312.

It is a junction number, because it is equal to n+sod(n) for n = 21355120499 and 21355120508.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21355120541) by changing a digit.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 39681 + ... + 210439.

It is an arithmetic number, because the mean of its divisors is an integer number (692687940).

Almost surely, 2^21355120540 is an apocalyptic number.

21355120540 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 21355120540, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (24936765840).

21355120540 is an abundant number, since it is smaller than the sum of its proper divisors (28518411140).

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

21355120540 is a wasteful number, since it uses less digits than its factorization.

21355120540 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 170831 (or 170816 counting only the distinct ones).

The product of its (nonzero) digits is 6000, while the sum is 28.

Adding to 21355120540 its reverse (4502155312), we get a palindrome (25857275852).

The spelling of 21355120540 in words is "twenty-one billion, three hundred fifty-five million, one hundred twenty thousand, five hundred forty".