12921721 has 4 divisors (see below), whose sum is σ = 12928912. Its totient is φ = 12914532.

The previous prime is 12921679. The next prime is 12921763. The reversal of 12921721 is 12712921.

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 a brilliant number, because the two primes have the same length.

It is an interprime number because it is at equal distance from previous prime (12921679) and next prime (12921763).

It is a cyclic number.

It is not a de Polignac number, because 12921721 - 2¹³ = 12913529 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (12924721) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 1726 + ... + 5368.

It is an arithmetic number, because the mean of its divisors is an integer number (3232228).

Almost surely, 2^12921721 is an apocalyptic number.

It is an amenable number.

12921721 is a deficient number, since it is larger than the sum of its proper divisors (7191).

12921721 is an equidigital number, since it uses as much as digits as its factorization.

12921721 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 7190.

The product of its digits is 504, while the sum is 25.

The square root of 12921721 is about 3594.6795406545. The cubic root of 12921721 is about 234.6605692699.

The spelling of 12921721 in words is "twelve million, nine hundred twenty-one thousand, seven hundred twenty-one".