21242643 has 4 divisors (see below), whose sum is σ = 28323528. Its totient is φ = 14161760.

The previous prime is 21242629. The next prime is 21242651. The reversal of 21242643 is 34624212.

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

It is a cyclic number.

It is not a de Polignac number, because 21242643 - 2⁹ = 21242131 is a prime.

It is not an unprimeable number, because it can be changed into a prime (21242443) 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, 3540438 + ... + 3540443.

It is an arithmetic number, because the mean of its divisors is an integer number (7080882).

Almost surely, 2^21242643 is an apocalyptic number.

21242643 is a deficient number, since it is larger than the sum of its proper divisors (7080885).

21242643 is an equidigital number, since it uses as much as digits as its factorization.

21242643 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 7080884.

The product of its digits is 2304, while the sum is 24.

The square root of 21242643 is about 4608.9741808780. The cubic root of 21242643 is about 276.9509442338.

Adding to 21242643 its reverse (34624212), we get a palindrome (55866855).

The spelling of 21242643 in words is "twenty-one million, two hundred forty-two thousand, six hundred forty-three".