12400021 has 4 divisors (see below), whose sum is σ = 13129452. Its totient is φ = 11670592.

The previous prime is 12400009. The next prime is 12400043. The reversal of 12400021 is 12000421.

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

It can be written as a sum of positive squares in 2 ways, for example, as 10400625 + 1999396 = 3225^2 + 1414^2 .

It is a cyclic number.

It is not a de Polignac number, because 12400021 - 2¹⁹ = 11875733 is a prime.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 12399980 and 12400007.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (12400001) 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, 364690 + ... + 364723.

It is an arithmetic number, because the mean of its divisors is an integer number (3282363).

Almost surely, 2^12400021 is an apocalyptic number.

It is an amenable number.

12400021 is a deficient number, since it is larger than the sum of its proper divisors (729431).

12400021 is an equidigital number, since it uses as much as digits as its factorization.

12400021 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 729430.

The product of its (nonzero) digits is 16, while the sum is 10.

The square root of 12400021 is about 3521.3663541302. The cubic root of 12400021 is about 231.4590361148.

Adding to 12400021 its reverse (12000421), we get a palindrome (24400442).

The spelling of 12400021 in words is "twelve million, four hundred thousand, twenty-one".