21105021 has 16 divisors (see below), whose sum is σ = 32845824. Its totient is φ = 11802864.

The previous prime is 21105013. The next prime is 21105023. The reversal of 21105021 is 12050112.

It is not a de Polignac number, because 21105021 - 2³ = 21105013 is a prime.

It is a super-2 number, since 2×21105021² = 890843822820882, which contains 22 as substring.

It is a junction number, because it is equal to n+sod(n) for n = 21104988 and 21105006.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21105023) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 9705 + ... + 11678.

It is an arithmetic number, because the mean of its divisors is an integer number (2052864).

Almost surely, 2^21105021 is an apocalyptic number.

21105021 is a gapful number since it is divisible by the number (21) formed by its first and last digit.

It is an amenable number.

21105021 is a deficient number, since it is larger than the sum of its proper divisors (11740803).

21105021 is a wasteful number, since it uses less digits than its factorization.

21105021 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 21440.

The product of its (nonzero) digits is 20, while the sum is 12.

The square root of 21105021 is about 4594.0201349145. The cubic root of 21105021 is about 276.3515657469.

Adding to 21105021 its reverse (12050112), we get a palindrome (33155133).

The spelling of 21105021 in words is "twenty-one million, one hundred five thousand, twenty-one".