13681721 has 2 divisors, whose sum is σ = 13681722. Its totient is φ = 13681720.

The previous prime is 13681709. The next prime is 13681727. The reversal of 13681721 is 12718631.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 6864400 + 6817321 = 2620^2 + 2611^2 .

It is an emirp because it is prime and its reverse (12718631) is a distict prime.

It is a cyclic number.

It is not a de Polignac number, because 13681721 - 2¹⁰ = 13680697 is a prime.

It is a Chen prime.

It is not a weakly prime, because it can be changed into another prime (13681727) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 6840860 + 6840861.

It is an arithmetic number, because the mean of its divisors is an integer number (6840861).

Almost surely, 2^13681721 is an apocalyptic number.

It is an amenable number.

13681721 is a deficient number, since it is larger than the sum of its proper divisors (1).

13681721 is an equidigital number, since it uses as much as digits as its factorization.

13681721 is an evil number, because the sum of its binary digits is even.

The product of its digits is 2016, while the sum is 29.

The square root of 13681721 is about 3698.8810470195. The cubic root of 13681721 is about 239.1737851254.

The spelling of 13681721 in words is "thirteen million, six hundred eighty-one thousand, seven hundred twenty-one".