21045663 has 10 divisors (see below), whose sum is σ = 31438704. Its totient is φ = 14030388.

The previous prime is 21045649. The next prime is 21045691. The reversal of 21045663 is 36654012.

It is not a de Polignac number, because 21045663 - 2⁶ = 21045599 is a prime.

It is a super-2 number, since 2×21045663² = 885839862219138, which contains 22 as substring.

It is a Harshad number since it is a multiple of its sum of digits (27).

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21045263) 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 9 ways as a sum of consecutive naturals, for example, 129831 + ... + 129992.

Almost surely, 2^21045663 is an apocalyptic number.

21045663 is a deficient number, since it is larger than the sum of its proper divisors (10393041).

21045663 is an equidigital number, since it uses as much as digits as its factorization.

21045663 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 259835 (or 259826 counting only the distinct ones).

The product of its (nonzero) digits is 4320, while the sum is 27.

The square root of 21045663 is about 4587.5552312752. Note that the first 3 decimals coincide. The cubic root of 21045663 is about 276.0922423250.

Adding to 21045663 its reverse (36654012), we get a palindrome (57699675).

The spelling of 21045663 in words is "twenty-one million, forty-five thousand, six hundred sixty-three".