21207451 has 4 divisors (see below), whose sum is σ = 21222432. Its totient is φ = 21192472.

The previous prime is 21207437. The next prime is 21207467. The reversal of 21207451 is 15470212.

It is a happy number.

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 21207451 - 2¹³ = 21199259 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21207421) 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 3 ways as a sum of consecutive naturals, for example, 5116 + ... + 8281.

It is an arithmetic number, because the mean of its divisors is an integer number (5305608).

Almost surely, 2^21207451 is an apocalyptic number.

21207451 is a deficient number, since it is larger than the sum of its proper divisors (14981).

21207451 is a wasteful number, since it uses less digits than its factorization.

21207451 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 14980.

The product of its (nonzero) digits is 560, while the sum is 22.

The square root of 21207451 is about 4605.1548291018. The cubic root of 21207451 is about 276.7979211408.

Adding to 21207451 its reverse (15470212), we get a palindrome (36677663).

The spelling of 21207451 in words is "twenty-one million, two hundred seven thousand, four hundred fifty-one".