12721805 has 4 divisors (see below), whose sum is σ = 15266172. Its totient is φ = 10177440.

The previous prime is 12721801. The next prime is 12721843. The reversal of 12721805 is 50812721.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 50812721 = 79 ⋅643199.

It can be written as a sum of positive squares in 2 ways, for example, as 8649481 + 4072324 = 2941^2 + 2018^2 .

It is not a de Polignac number, because 12721805 - 2² = 12721801 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 (12721801) 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, 1272176 + ... + 1272185.

It is an arithmetic number, because the mean of its divisors is an integer number (3816543).

Almost surely, 2^12721805 is an apocalyptic number.

It is an amenable number.

12721805 is a deficient number, since it is larger than the sum of its proper divisors (2544367).

12721805 is an equidigital number, since it uses as much as digits as its factorization.

12721805 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2544366.

The product of its (nonzero) digits is 1120, while the sum is 26.

The square root of 12721805 is about 3566.7639394835. The cubic root of 12721805 is about 233.4441050008. Note that the first 3 decimals are identical.

The spelling of 12721805 in words is "twelve million, seven hundred twenty-one thousand, eight hundred five".