168643921 has 4 divisors (see below), whose sum is σ = 168781492. Its totient is φ = 168506352.

The previous prime is 168643919. The next prime is 168643931. The reversal of 168643921 is 129346861.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 129346861 = 7 ⋅18478123.

It can be written as a sum of positive squares in 2 ways, for example, as 52780225 + 115863696 = 7265^2 + 10764^2 .

It is a cyclic number.

It is not a de Polignac number, because 168643921 - 2¹ = 168643919 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (168643931) 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, 66930 + ... + 69403.

It is an arithmetic number, because the mean of its divisors is an integer number (42195373).

Almost surely, 2^168643921 is an apocalyptic number.

It is an amenable number.

168643921 is a deficient number, since it is larger than the sum of its proper divisors (137571).

168643921 is a wasteful number, since it uses less digits than its factorization.

168643921 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 137570.

The product of its digits is 62208, while the sum is 40.

The square root of 168643921 is about 12986.2974322938. The cubic root of 168643921 is about 552.4889084128.

The spelling of 168643921 in words is "one hundred sixty-eight million, six hundred forty-three thousand, nine hundred twenty-one".