158991721 has 6 divisors (see below), whose sum is σ = 184949610. Its totient is φ = 136278576.

The previous prime is 158991719. The next prime is 158991731. The reversal of 158991721 is 127199851.

It can be written as a sum of positive squares in only one way, i.e., 149719696 + 9272025 = 12236^2 + 3045^2 .

It is not a de Polignac number, because 158991721 - 2¹ = 158991719 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (158991731) 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 5 ways as a sum of consecutive naturals, for example, 1622316 + ... + 1622413.

It is an arithmetic number, because the mean of its divisors is an integer number (30824935).

Almost surely, 2^158991721 is an apocalyptic number.

It is an amenable number.

158991721 is a deficient number, since it is larger than the sum of its proper divisors (25957889).

158991721 is an equidigital number, since it uses as much as digits as its factorization.

158991721 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 3244743 (or 3244736 counting only the distinct ones).

The product of its digits is 45360, while the sum is 43.

The square root of 158991721 is about 12609.1919249411. The cubic root of 158991721 is about 541.7407485054.

It can be divided in two parts, 158991 and 721, that multiplied together give a triangular number (114632511 = T₁₅₁₄₁).

The spelling of 158991721 in words is "one hundred fifty-eight million, nine hundred ninety-one thousand, seven hundred twenty-one".