21021275520 has 640 divisors, whose sum is σ = 87493919040. Its totient is φ = 4709892096.

The previous prime is 21021275503. The next prime is 21021275521. The reversal of 21021275520 is 2557212012.

21021275520 is a `hidden beast` number, since 2 + 10 + 2 + 127 + 5 + 520 = 666.

It is a tau number, because it is divible by the number of its divisors (640).

It is a Harshad number since it is a multiple of its sum of digits (27).

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21021275521) 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 79 ways as a sum of consecutive naturals, for example, 19232094 + ... + 19233186.

Almost surely, 2^21021275520 is an apocalyptic number.

21021275520 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 21021275520, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (43746959520).

21021275520 is an abundant number, since it is smaller than the sum of its proper divisors (66472643520).

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

21021275520 is a wasteful number, since it uses less digits than its factorization.

21021275520 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1184 (or 1163 counting only the distinct ones).

The product of its (nonzero) digits is 2800, while the sum is 27.

Adding to 21021275520 its reverse (2557212012), we get a palindrome (23578487532).

The spelling of 21021275520 in words is "twenty-one billion, twenty-one million, two hundred seventy-five thousand, five hundred twenty".