309921 has 4 divisors (see below), whose sum is σ = 413232. Its totient is φ = 206612.

The previous prime is 309899. The next prime is 309929. The reversal of 309921 is 129903.

It is a happy number.

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.

It is a cyclic number.

It is not a de Polignac number, because 309921 - 2⁶ = 309857 is a prime.

It is a D-number.

309921 is a lucky number.

It is a junction number, because it is equal to n+sod(n) for n = 309891 and 309900.

It is an inconsummate number, since it does not exist a number n which divided by its sum of digits gives 309921.

It is not an unprimeable number, because it can be changed into a prime (309929) 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, 51651 + ... + 51656.

It is an arithmetic number, because the mean of its divisors is an integer number (103308).

2³⁰⁹⁹²¹ is an apocalyptic number.

It is an amenable number.

309921 is a deficient number, since it is larger than the sum of its proper divisors (103311).

309921 is a wasteful number, since it uses less digits than its factorization.

309921 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 103310.

The product of its (nonzero) digits is 486, while the sum is 24.

The square root of 309921 is about 556.7054876683. The cubic root of 309921 is about 67.6732449568.

The spelling of 309921 in words is "three hundred nine thousand, nine hundred twenty-one".