12721921 has 6 divisors (see below), whose sum is σ = 13299650. Its totient is φ = 12168288.

The previous prime is 12721903. The next prime is 12721939. The reversal of 12721921 is 12912721.

It is an interprime number because it is at equal distance from previous prime (12721903) and next prime (12721939).

It can be written as a sum of positive squares in only one way, i.e., 10817521 + 1904400 = 3289^2 + 1380^2 .

It is a de Polignac number, because none of the positive numbers 2^k-12721921 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (12721721) by changing a digit.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 11496 + ... + 12553.

Almost surely, 2^12721921 is an apocalyptic number.

It is an amenable number.

12721921 is a deficient number, since it is larger than the sum of its proper divisors (577729).

12721921 is an equidigital number, since it uses as much as digits as its factorization.

12721921 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 24095 (or 24072 counting only the distinct ones).

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

The square root of 12721921 is about 3566.7802006852. The cubic root of 12721921 is about 233.4448145289. Note that the first 3 decimals are identical.

The spelling of 12721921 in words is "twelve million, seven hundred twenty-one thousand, nine hundred twenty-one".