21243566 has 16 divisors (see below), whose sum is σ = 32787504. Its totient is φ = 10318464.

The previous prime is 21243533. The next prime is 21243581. The reversal of 21243566 is 66534212.

It is a congruent number.

It is an unprimeable number.

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 7 ways as a sum of consecutive naturals, for example, 10406 + ... + 12278.

It is an arithmetic number, because the mean of its divisors is an integer number (2049219).

Almost surely, 2^21243566 is an apocalyptic number.

21243566 is a deficient number, since it is larger than the sum of its proper divisors (11543938).

21243566 is a wasteful number, since it uses less digits than its factorization.

21243566 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2035.

The product of its digits is 8640, while the sum is 29.

The square root of 21243566 is about 4609.0743105313. The cubic root of 21243566 is about 276.9549553797.

Adding to 21243566 its reverse (66534212), we get a palindrome (87777778).

The spelling of 21243566 in words is "twenty-one million, two hundred forty-three thousand, five hundred sixty-six".