15717991 has 4 divisors (see below), whose sum is σ = 15738184. Its totient is φ = 15697800.

The previous prime is 15717973. The next prime is 15718009. The reversal of 15717991 is 19971751.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 19971751 = 23 ⋅868337.

It is an interprime number because it is at equal distance from previous prime (15717973) and next prime (15718009).

It is a cyclic number.

It is not a de Polignac number, because 15717991 - 2¹⁵ = 15685223 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (15717941) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 8880 + ... + 10501.

It is an arithmetic number, because the mean of its divisors is an integer number (3934546).

Almost surely, 2^15717991 is an apocalyptic number.

15717991 is a deficient number, since it is larger than the sum of its proper divisors (20193).

15717991 is an equidigital number, since it uses as much as digits as its factorization.

15717991 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 20192.

The product of its digits is 19845, while the sum is 40.

The square root of 15717991 is about 3964.5921606137. The cubic root of 15717991 is about 250.4949713666.

The spelling of 15717991 in words is "fifteen million, seven hundred seventeen thousand, nine hundred ninety-one".