13215721 has 2 divisors, whose sum is σ = 13215722. Its totient is φ = 13215720.

The previous prime is 13215707. The next prime is 13215739. The reversal of 13215721 is 12751231.

It is a happy number.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 13039321 + 176400 = 3611^2 + 420^2 .

It is an emirp because it is prime and its reverse (12751231) is a distict prime.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-13215721 is a prime.

It is a junction number, because it is equal to n+sod(n) for n = 13215692 and 13215701.

It is not a weakly prime, because it can be changed into another prime (13215751) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 6607860 + 6607861.

It is an arithmetic number, because the mean of its divisors is an integer number (6607861).

Almost surely, 2^13215721 is an apocalyptic number.

It is an amenable number.

13215721 is a deficient number, since it is larger than the sum of its proper divisors (1).

13215721 is an equidigital number, since it uses as much as digits as its factorization.

13215721 is an evil number, because the sum of its binary digits is even.

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

The square root of 13215721 is about 3635.3433125360. The cubic root of 13215721 is about 236.4269359378.

Adding to 13215721 its reverse (12751231), we get a palindrome (25966952).

The spelling of 13215721 in words is "thirteen million, two hundred fifteen thousand, seven hundred twenty-one".