13666721 has 2 divisors, whose sum is σ = 13666722. Its totient is φ = 13666720.

The previous prime is 13666717. The next prime is 13666729. The reversal of 13666721 is 12766631.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 7639696 + 6027025 = 2764^2 + 2455^2 .

It is a cyclic number.

It is not a de Polignac number, because 13666721 - 2² = 13666717 is a prime.

It is not a weakly prime, because it can be changed into another prime (13666729) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 6833360 + 6833361.

It is an arithmetic number, because the mean of its divisors is an integer number (6833361).

Almost surely, 2^13666721 is an apocalyptic number.

It is an amenable number.

13666721 is a deficient number, since it is larger than the sum of its proper divisors (1).

13666721 is an equidigital number, since it uses as much as digits as its factorization.

13666721 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 9072, while the sum is 32.

The square root of 13666721 is about 3696.8528507367. The cubic root of 13666721 is about 239.0863468401.

The spelling of 13666721 in words is "thirteen million, six hundred sixty-six thousand, seven hundred twenty-one".