15917221 has 2 divisors, whose sum is σ = 15917222. Its totient is φ = 15917220.

The previous prime is 15917203. The next prime is 15917243. The reversal of 15917221 is 12271951.

15917221 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 15602500 + 314721 = 3950^2 + 561^2 .

It is an emirp because it is prime and its reverse (12271951) is a distict prime.

It is a cyclic number.

It is not a de Polignac number, because 15917221 - 2⁷ = 15917093 is a prime.

It is a self number, because there is not a number n which added to its sum of digits gives 15917221.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (15917281) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 7958610 + 7958611.

It is an arithmetic number, because the mean of its divisors is an integer number (7958611).

Almost surely, 2^15917221 is an apocalyptic number.

It is an amenable number.

15917221 is a deficient number, since it is larger than the sum of its proper divisors (1).

15917221 is an equidigital number, since it uses as much as digits as its factorization.

15917221 is an evil number, because the sum of its binary digits is even.

The product of its digits is 1260, while the sum is 28.

The square root of 15917221 is about 3989.6392067454. The cubic root of 15917221 is about 251.5488958681.

The spelling of 15917221 in words is "fifteen million, nine hundred seventeen thousand, two hundred twenty-one".