21105520 has 20 divisors (see below), whose sum is σ = 49070520. Its totient is φ = 8442176.

The previous prime is 21105509. The next prime is 21105547. The reversal of 21105520 is 2550112.

It is a tau number, because it is divible by the number of its divisors (20).

It is a Harshad number since it is a multiple of its sum of digits (16).

It is a junction number, because it is equal to n+sod(n) for n = 21105494 and 21105503.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 131830 + ... + 131989.

It is an arithmetic number, because the mean of its divisors is an integer number (2453526).

Almost surely, 2^21105520 is an apocalyptic number.

21105520 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21105520 is an abundant number, since it is smaller than the sum of its proper divisors (27965000).

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

21105520 is a wasteful number, since it uses less digits than its factorization.

21105520 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 263832 (or 263826 counting only the distinct ones).

The product of its (nonzero) digits is 100, while the sum is 16.

The square root of 21105520 is about 4594.0744443250. The cubic root of 21105520 is about 276.3537437175.

Adding to 21105520 its reverse (2550112), we get a palindrome (23655632).

The spelling of 21105520 in words is "twenty-one million, one hundred five thousand, five hundred twenty".