15900721 has 2 divisors, whose sum is σ = 15900722. Its totient is φ = 15900720.

The previous prime is 15900719. The next prime is 15900757. The reversal of 15900721 is 12700951.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 14930496 + 970225 = 3864^2 + 985^2 .

It is a cyclic number.

It is not a de Polignac number, because 15900721 - 2¹ = 15900719 is a prime.

Together with 15900719, it forms a pair of twin primes.

It is not a weakly prime, because it can be changed into another prime (15900761) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 7950360 + 7950361.

It is an arithmetic number, because the mean of its divisors is an integer number (7950361).

Almost surely, 2^15900721 is an apocalyptic number.

It is an amenable number.

15900721 is a deficient number, since it is larger than the sum of its proper divisors (1).

15900721 is an equidigital number, since it uses as much as digits as its factorization.

15900721 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 630, while the sum is 25.

The square root of 15900721 is about 3987.5708144182. The cubic root of 15900721 is about 251.4619461888.

The spelling of 15900721 in words is "fifteen million, nine hundred thousand, seven hundred twenty-one".