165421661 has 4 divisors (see below), whose sum is σ = 165784092. Its totient is φ = 165059232.

The previous prime is 165421621. The next prime is 165421687. The reversal of 165421661 is 166124561.

165421661 = 359² + 360² + ... + 815².

165421661 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 131560900 + 33860761 = 11470^2 + 5819^2 .

It is a cyclic number.

It is not a de Polignac number, because 165421661 - 2¹⁰ = 165420637 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 (165421601) 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, 180530 + ... + 181443.

It is an arithmetic number, because the mean of its divisors is an integer number (41446023).

Almost surely, 2^165421661 is an apocalyptic number.

It is an amenable number.

165421661 is a deficient number, since it is larger than the sum of its proper divisors (362431).

165421661 is an equidigital number, since it uses as much as digits as its factorization.

165421661 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 362430.

The product of its digits is 8640, while the sum is 32.

The square root of 165421661 is about 12861.6352381803. The cubic root of 165421661 is about 548.9474757952.

The spelling of 165421661 in words is "one hundred sixty-five million, four hundred twenty-one thousand, six hundred sixty-one".