21125421 has 16 divisors (see below), whose sum is σ = 31372800. Its totient is φ = 14049504.

The previous prime is 21125393. The next prime is 21125443. The reversal of 21125421 is 12452112.

It is not a de Polignac number, because 21125421 - 2⁵ = 21125389 is a prime.

It is a Curzon number.

It is a junction number, because it is equal to n+sod(n) for n = 21125394 and 21125403.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21125471) 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 15 ways as a sum of consecutive naturals, for example, 15745 + ... + 17033.

It is an arithmetic number, because the mean of its divisors is an integer number (1960800).

Almost surely, 2^21125421 is an apocalyptic number.

It is an amenable number.

21125421 is a deficient number, since it is larger than the sum of its proper divisors (10247379).

21125421 is a wasteful number, since it uses less digits than its factorization.

21125421 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1905 (or 1899 counting only the distinct ones).

The product of its digits is 160, while the sum is 18.

The square root of 21125421 is about 4596.2398762467. The cubic root of 21125421 is about 276.4405770538.

Adding to 21125421 its reverse (12452112), we get a palindrome (33577533).

The spelling of 21125421 in words is "twenty-one million, one hundred twenty-five thousand, four hundred twenty-one".