15997921 has 4 divisors (see below), whose sum is σ = 16260244. Its totient is φ = 15735600.

The previous prime is 15997889. The next prime is 15997957. The reversal of 15997921 is 12979951.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 12979951 = 769 ⋅16879.

It can be written as a sum of positive squares in 2 ways, for example, as 5239521 + 10758400 = 2289^2 + 3280^2 .

It is a cyclic number.

It is not a de Polignac number, because 15997921 - 2⁵ = 15997889 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (15997021) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 131070 + ... + 131191.

It is an arithmetic number, because the mean of its divisors is an integer number (4065061).

Almost surely, 2^15997921 is an apocalyptic number.

It is an amenable number.

15997921 is a deficient number, since it is larger than the sum of its proper divisors (262323).

15997921 is an equidigital number, since it uses as much as digits as its factorization.

15997921 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 262322.

The product of its digits is 51030, while the sum is 43.

The square root of 15997921 is about 3999.7401165576. The cubic root of 15997921 is about 251.9732954401.

It can be divided in two parts, 159979 and 21, that added together give a 4-th power (160000 = 20⁴).

The spelling of 15997921 in words is "fifteen million, nine hundred ninety-seven thousand, nine hundred twenty-one".