168406721 has 16 divisors (see below), whose sum is σ = 202500480. Its totient is φ = 137013120.

The previous prime is 168406697. The next prime is 168406727. The reversal of 168406721 is 127604861.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-168406721 is a prime.

It is not an unprimeable number, because it can be changed into a prime (168406727) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 2690 + ... + 18548.

It is an arithmetic number, because the mean of its divisors is an integer number (12656280).

Almost surely, 2^168406721 is an apocalyptic number.

It is an amenable number.

168406721 is a deficient number, since it is larger than the sum of its proper divisors (34093759).

168406721 is a wasteful number, since it uses less digits than its factorization.

168406721 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 15944.

The product of its (nonzero) digits is 16128, while the sum is 35.

The square root of 168406721 is about 12977.1615155241. The cubic root of 168406721 is about 552.2297591202.

The spelling of 168406721 in words is "one hundred sixty-eight million, four hundred six thousand, seven hundred twenty-one".