21206447 has 4 divisors (see below), whose sum is σ = 21657696. Its totient is φ = 20755200.

The previous prime is 21206443. The next prime is 21206477. The reversal of 21206447 is 74460212.

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

It is not a de Polignac number, because 21206447 - 2² = 21206443 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21206441) 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, 225554 + ... + 225647.

It is an arithmetic number, because the mean of its divisors is an integer number (5414424).

Almost surely, 2^21206447 is an apocalyptic number.

21206447 is a deficient number, since it is larger than the sum of its proper divisors (451249).

21206447 is an equidigital number, since it uses as much as digits as its factorization.

21206447 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 451248.

The product of its (nonzero) digits is 2688, while the sum is 26.

The square root of 21206447 is about 4605.0458195332. The cubic root of 21206447 is about 276.7935530299.

Adding to 21206447 its reverse (74460212), we get a palindrome (95666659).

The spelling of 21206447 in words is "twenty-one million, two hundred six thousand, four hundred forty-seven".