165903821 has 4 divisors (see below), whose sum is σ = 167454432. Its totient is φ = 164353212.

The previous prime is 165903797. The next prime is 165903827. The reversal of 165903821 is 128309561.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4, and also an emirpimes, since its reverse is a distinct semiprime: 128309561 = 3923 ⋅32707.

It is a cyclic number.

It is not a de Polignac number, because 165903821 - 2⁶ = 165903757 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 (165903827) 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, 775145 + ... + 775358.

It is an arithmetic number, because the mean of its divisors is an integer number (41863608).

Almost surely, 2^165903821 is an apocalyptic number.

It is an amenable number.

165903821 is a deficient number, since it is larger than the sum of its proper divisors (1550611).

165903821 is a wasteful number, since it uses less digits than its factorization.

165903821 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1550610.

The product of its (nonzero) digits is 12960, while the sum is 35.

The square root of 165903821 is about 12880.3657168576. The cubic root of 165903821 is about 549.4803035825.

The spelling of 165903821 in words is "one hundred sixty-five million, nine hundred three thousand, eight hundred twenty-one".