13521721 has 4 divisors (see below), whose sum is σ = 13542372. Its totient is φ = 13501072.

The previous prime is 13521713. The next prime is 13521727. The reversal of 13521721 is 12712531.

It is a happy number.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 10497600 + 3024121 = 3240^2 + 1739^2 .

It is a cyclic number.

It is not a de Polignac number, because 13521721 - 2³ = 13521713 is a prime.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 13521692 and 13521701.

It is not an unprimeable number, because it can be changed into a prime (13521727) 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, 9310 + ... + 10663.

It is an arithmetic number, because the mean of its divisors is an integer number (3385593).

Almost surely, 2^13521721 is an apocalyptic number.

It is an amenable number.

13521721 is a deficient number, since it is larger than the sum of its proper divisors (20651).

13521721 is an equidigital number, since it uses as much as digits as its factorization.

13521721 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 20650.

The product of its digits is 420, while the sum is 22.

The square root of 13521721 is about 3677.1892798712. The cubic root of 13521721 is about 238.2377928413.

The spelling of 13521721 in words is "thirteen million, five hundred twenty-one thousand, seven hundred twenty-one".