165621421 has 12 divisors (see below), whose sum is σ = 193165020. Its totient is φ = 141590400.

The previous prime is 165621409. The next prime is 165621433. The reversal of 165621421 is 124126561.

It is an interprime number because it is at equal distance from previous prime (165621409) and next prime (165621433).

It can be written as a sum of positive squares in 2 ways, for example, as 108784900 + 56836521 = 10430^2 + 7539^2 .

It is not a de Polignac number, because 165621421 - 2⁹ = 165620909 is a prime.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 165621421.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (165621121) by changing a digit.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 15435 + ... + 23863.

It is an arithmetic number, because the mean of its divisors is an integer number (16097085).

Almost surely, 2^165621421 is an apocalyptic number.

It is an amenable number.

165621421 is a deficient number, since it is larger than the sum of its proper divisors (27543599).

165621421 is an equidigital number, since it uses as much as digits as its factorization.

165621421 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 8844 (or 8837 counting only the distinct ones).

The product of its digits is 2880, while the sum is 28.

The square root of 165621421 is about 12869.3986261985. The cubic root of 165621421 is about 549.1683530299.

Adding to 165621421 its reverse (124126561), we get a palindrome (289747982).

The spelling of 165621421 in words is "one hundred sixty-five million, six hundred twenty-one thousand, four hundred twenty-one".