21121255520 has 48 divisors (see below), whose sum is σ = 49982220288. Its totient is φ = 8434406400.

The previous prime is 21121255517. The next prime is 21121255577. The reversal of 21121255520 is 2555212112.

It is a happy number.

It is a super-2 number, since 2×21121255520² (a number of 21 digits) contains 22 as substring.

It is a self number, because there is not a number n which added to its sum of digits gives 21121255520.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 13664 + ... + 205983.

It is an arithmetic number, because the mean of its divisors is an integer number (1041296256).

Almost surely, 2^21121255520 is an apocalyptic number.

21121255520 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21121255520 is an abundant number, since it is smaller than the sum of its proper divisors (28860964768).

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

21121255520 is a wasteful number, since it uses less digits than its factorization.

21121255520 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 220263 (or 220255 counting only the distinct ones).

The product of its (nonzero) digits is 2000, while the sum is 26.

Adding to 21121255520 its reverse (2555212112), we get a palindrome (23676467632).

The spelling of 21121255520 in words is "twenty-one billion, one hundred twenty-one million, two hundred fifty-five thousand, five hundred twenty".