12720021 has 4 divisors (see below), whose sum is σ = 16960032. Its totient is φ = 8480012.

The previous prime is 12720011. The next prime is 12720047. The reversal of 12720021 is 12002721.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4, and also an emirpimes, since its reverse is a distinct semiprime: 12002721 = 3 ⋅4000907.

It is a cyclic number.

It is not a de Polignac number, because 12720021 - 2¹⁴ = 12703637 is a prime.

It is a Curzon number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (12720011) 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, 2120001 + ... + 2120006.

It is an arithmetic number, because the mean of its divisors is an integer number (4240008).

Almost surely, 2^12720021 is an apocalyptic number.

It is an amenable number.

12720021 is a deficient number, since it is larger than the sum of its proper divisors (4240011).

12720021 is an equidigital number, since it uses as much as digits as its factorization.

12720021 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 4240010.

The product of its (nonzero) digits is 56, while the sum is 15.

The square root of 12720021 is about 3566.5138440780. The cubic root of 12720021 is about 233.4331924049.

Adding to 12720021 its reverse (12002721), we get a palindrome (24722742).

The spelling of 12720021 in words is "twelve million, seven hundred twenty thousand, twenty-one".