21240442 has 16 divisors (see below), whose sum is σ = 34446240. Its totient is φ = 9788688.

The previous prime is 21240433. The next prime is 21240511. The reversal of 21240442 is 24404212.

It is a Harshad number since it is a multiple of its sum of digits (19).

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, 6148 + ... + 8959.

It is an arithmetic number, because the mean of its divisors is an integer number (2152890).

Almost surely, 2^21240442 is an apocalyptic number.

21240442 is a deficient number, since it is larger than the sum of its proper divisors (13205798).

21240442 is a wasteful number, since it uses less digits than its factorization.

21240442 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 15165.

The product of its (nonzero) digits is 512, while the sum is 19.

The square root of 21240442 is about 4608.7354013872. The cubic root of 21240442 is about 276.9413787247.

Adding to 21240442 its reverse (24404212), we get a palindrome (45644654).

The spelling of 21240442 in words is "twenty-one million, two hundred forty thousand, four hundred forty-two".