8515721 has 2 divisors, whose sum is σ = 8515722. Its totient is φ = 8515720.

The previous prime is 8515711. The next prime is 8515723. The reversal of 8515721 is 1275158.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 8497225 + 18496 = 2915^2 + 136^2 .

It is a cyclic number.

It is not a de Polignac number, because 8515721 - 2¹⁰ = 8514697 is a prime.

Together with 8515723, it forms a pair of twin primes.

It is a Chen prime.

It is not a weakly prime, because it can be changed into another prime (8515723) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 4257860 + 4257861.

It is an arithmetic number, because the mean of its divisors is an integer number (4257861).

Almost surely, 2^8515721 is an apocalyptic number.

It is an amenable number.

8515721 is a deficient number, since it is larger than the sum of its proper divisors (1).

8515721 is an equidigital number, since it uses as much as digits as its factorization.

8515721 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 2800, while the sum is 29.

The square root of 8515721 is about 2918.1708311886. The cubic root of 8515721 is about 204.2084966261.

The spelling of 8515721 in words is "eight million, five hundred fifteen thousand, seven hundred twenty-one".