15642721 has 2 divisors, whose sum is σ = 15642722. Its totient is φ = 15642720.

The previous prime is 15642701. The next prime is 15642727. The reversal of 15642721 is 12724651.

15642721 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 15124321 + 518400 = 3889^2 + 720^2 .

It is an emirp because it is prime and its reverse (12724651) is a distict prime.

It is a cyclic number.

It is not a de Polignac number, because 15642721 - 2⁷ = 15642593 is a prime.

It is a self number, because there is not a number n which added to its sum of digits gives 15642721.

It is not a weakly prime, because it can be changed into another prime (15642727) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 7821360 + 7821361.

It is an arithmetic number, because the mean of its divisors is an integer number (7821361).

Almost surely, 2^15642721 is an apocalyptic number.

It is an amenable number.

15642721 is a deficient number, since it is larger than the sum of its proper divisors (1).

15642721 is an equidigital number, since it uses as much as digits as its factorization.

15642721 is an evil number, because the sum of its binary digits is even.

The product of its digits is 3360, while the sum is 28.

The square root of 15642721 is about 3955.0879889075. The cubic root of 15642721 is about 250.0944762924.

The spelling of 15642721 in words is "fifteen million, six hundred forty-two thousand, seven hundred twenty-one".