21240447 has 8 divisors (see below), whose sum is σ = 28662144. Its totient is φ = 13989528.

The previous prime is 21240433. The next prime is 21240511. The reversal of 21240447 is 74404212.

It is a sphenic number, since it is the product of 3 distinct primes.

It is not a de Polignac number, because 21240447 - 2²² = 17046143 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21240547) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 42403 + ... + 42900.

It is an arithmetic number, because the mean of its divisors is an integer number (3582768).

Almost surely, 2^21240447 is an apocalyptic number.

21240447 is a deficient number, since it is larger than the sum of its proper divisors (7421697).

21240447 is an equidigital number, since it uses as much as digits as its factorization.

21240447 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 85389.

The product of its (nonzero) digits is 1792, while the sum is 24.

The square root of 21240447 is about 4608.7359438354. The cubic root of 21240447 is about 276.9414004554.

Adding to 21240447 its reverse (74404212), we get a palindrome (95644659).

The spelling of 21240447 in words is "twenty-one million, two hundred forty thousand, four hundred forty-seven".