21045817 has 4 divisors (see below), whose sum is σ = 22664740. Its totient is φ = 19426896.

The previous prime is 21045811. The next prime is 21045853. The reversal of 21045817 is 71854012.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 2547216 + 18498601 = 1596^2 + 4301^2 .

It is a cyclic number.

It is not a de Polignac number, because 21045817 - 2³ = 21045809 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21045811) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 809442 + ... + 809467.

It is an arithmetic number, because the mean of its divisors is an integer number (5666185).

Almost surely, 2^21045817 is an apocalyptic number.

It is an amenable number.

21045817 is a deficient number, since it is larger than the sum of its proper divisors (1618923).

21045817 is a wasteful number, since it uses less digits than its factorization.

21045817 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1618922.

The product of its (nonzero) digits is 2240, while the sum is 28.

The square root of 21045817 is about 4587.5720157835. The cubic root of 21045817 is about 276.0929157512.

Adding to 21045817 its reverse (71854012), we get a palindrome (92899829).

It can be divided in two parts, 2104 and 5817, that added together give a square (7921 = 89²).

The spelling of 21045817 in words is "twenty-one million, forty-five thousand, eight hundred seventeen".