15993661 has 4 divisors (see below), whose sum is σ = 16264800. Its totient is φ = 15722524.

The previous prime is 15993647. The next prime is 15993689. The reversal of 15993661 is 16639951.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is not a de Polignac number, because 15993661 - 2¹⁹ = 15469373 is a prime.

It is a Smith number, since the sum of its digits (40) coincides with the sum of the digits of its prime factors. Since it is squarefree, it is also a hoax number.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (15993631) 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, 135481 + ... + 135598.

It is an arithmetic number, because the mean of its divisors is an integer number (4066200).

Almost surely, 2^15993661 is an apocalyptic number.

15993661 is the 1789-th centered decagonal number.

It is an amenable number.

15993661 is a deficient number, since it is larger than the sum of its proper divisors (271139).

15993661 is an equidigital number, since it uses as much as digits as its factorization.

15993661 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 271138.

The product of its digits is 43740, while the sum is 40.

The square root of 15993661 is about 3999.2075465022. The cubic root of 15993661 is about 251.9509279185.

The spelling of 15993661 in words is "fifteen million, nine hundred ninety-three thousand, six hundred sixty-one".