165406821 has 8 divisors (see below), whose sum is σ = 233515584. Its totient is φ = 103784640.

The previous prime is 165406817. The next prime is 165406841. The reversal of 165406821 is 128604561.

It is a sphenic number, since it is the product of 3 distinct primes.

It is not a de Polignac number, because 165406821 - 2² = 165406817 is a prime.

It is a Smith number, since the sum of its digits (33) coincides with the sum of the digits of its prime factors. Since it is squarefree, it is also a hoax number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (165406811) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 1621585 + ... + 1621686.

It is an arithmetic number, because the mean of its divisors is an integer number (29189448).

Almost surely, 2^165406821 is an apocalyptic number.

It is an amenable number.

165406821 is a deficient number, since it is larger than the sum of its proper divisors (68108763).

165406821 is a wasteful number, since it uses less digits than its factorization.

165406821 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 3243291.

The product of its (nonzero) digits is 11520, while the sum is 33.

The square root of 165406821 is about 12861.0583157064. The cubic root of 165406821 is about 548.9310599197.

The spelling of 165406821 in words is "one hundred sixty-five million, four hundred six thousand, eight hundred twenty-one".