21056805 has 96 divisors (see below), whose sum is σ = 46725120. Its totient is φ = 8519040.

The previous prime is 21056801. The next prime is 21056831. The reversal of 21056805 is 50865012.

21056805 is a nontrivial binomial coefficient, being equal to C(6490, 2).

It is not a de Polignac number, because 21056805 - 2² = 21056801 is a prime.

It is a Curzon number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21056801) by changing a digit.

It is a polite number, since it can be written in 95 ways as a sum of consecutive naturals, for example, 204384 + ... + 204486.

It is an arithmetic number, because the mean of its divisors is an integer number (486720).

Almost surely, 2^21056805 is an apocalyptic number.

21056805 is the 6489-th triangular number and also the 3245-th hexagonal number.

It is an amenable number.

21056805 is an abundant number, since it is smaller than the sum of its proper divisors (25668315).

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

21056805 is a wasteful number, since it uses less digits than its factorization.

21056805 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 191 (or 188 counting only the distinct ones).

The product of its (nonzero) digits is 2400, while the sum is 27.

The square root of 21056805 is about 4588.7694428899. The cubic root of 21056805 is about 276.1409566698.

The spelling of 21056805 in words is "twenty-one million, fifty-six thousand, eight hundred five".