168991621 has 4 divisors (see below), whose sum is σ = 171513952. Its totient is φ = 166469292.

The previous prime is 168991619. The next prime is 168991631. The reversal of 168991621 is 126199861.

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 168991621 - 2¹ = 168991619 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 (168991631) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 1261065 + ... + 1261198.

It is an arithmetic number, because the mean of its divisors is an integer number (42878488).

Almost surely, 2^168991621 is an apocalyptic number.

It is an amenable number.

168991621 is a deficient number, since it is larger than the sum of its proper divisors (2522331).

168991621 is an equidigital number, since it uses as much as digits as its factorization.

168991621 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2522330.

The product of its digits is 46656, while the sum is 43.

The square root of 168991621 is about 12999.6777267746. The cubic root of 168991621 is about 552.8683440168.

The spelling of 168991621 in words is "one hundred sixty-eight million, nine hundred ninety-one thousand, six hundred twenty-one".