21125447 has 4 divisors (see below), whose sum is σ = 24143376. Its totient is φ = 18107520.

The previous prime is 21125443. The next prime is 21125471. The reversal of 21125447 is 74452112.

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 21125447 - 2² = 21125443 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 (21125443) by changing a digit.

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 3 ways as a sum of consecutive naturals, for example, 1508954 + ... + 1508967.

It is an arithmetic number, because the mean of its divisors is an integer number (6035844).

Almost surely, 2^21125447 is an apocalyptic number.

21125447 is a deficient number, since it is larger than the sum of its proper divisors (3017929).

21125447 is an equidigital number, since it uses as much as digits as its factorization.

21125447 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 3017928.

The product of its digits is 2240, while the sum is 26.

The square root of 21125447 is about 4596.2427046447. The cubic root of 21125447 is about 276.4406904630.

Adding to 21125447 its reverse (74452112), we get a palindrome (95577559).

The spelling of 21125447 in words is "twenty-one million, one hundred twenty-five thousand, four hundred forty-seven".