21663243 has 18 divisors (see below), whose sum is σ = 36400884. Its totient is φ = 12378744.

The previous prime is 21663227. The next prime is 21663247. The reversal of 21663243 is 34236612.

21663243 is a `hidden beast` number, since 21 + 6 + 632 + 4 + 3 = 666.

It is not a de Polignac number, because 21663243 - 2⁴ = 21663227 is a prime.

It is not an unprimeable number, because it can be changed into a prime (21663247) 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 17 ways as a sum of consecutive naturals, for example, 24121 + ... + 25002.

Almost surely, 2^21663243 is an apocalyptic number.

21663243 is a deficient number, since it is larger than the sum of its proper divisors (14737641).

21663243 is a wasteful number, since it uses less digits than its factorization.

21663243 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 49143 (or 49133 counting only the distinct ones).

The product of its digits is 5184, while the sum is 27.

The square root of 21663243 is about 4654.3789059336. The cubic root of 21663243 is about 278.7668688807.

Adding to 21663243 its reverse (34236612), we get a palindrome (55899855).

The spelling of 21663243 in words is "twenty-one million, six hundred sixty-three thousand, two hundred forty-three".