309 has 4 divisors (see below), whose sum is σ = 416. Its totient is φ = 204.

The previous prime is 307. The next prime is 311. The reversal of 309 is 903.

309 is nontrivially palindromic in base 9 and base 14.

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 an interprime number because it is at equal distance from previous prime (307) and next prime (311).

It is not a de Polignac number, because 309 - 2^{1} = 307 is a prime.

It is an Ulam number.

It is a D-number.

It is an alternating number because its digits alternate between odd and even.

It is a Duffinian number.

309 is an undulating number in base 9 and base 14.

309 is a modest number, since divided by 9 gives 3 as remainder.

It is a Curzon number.

It is a plaindrome in base 6, base 13, base 15 and base 16.

It is a nialpdrome in base 7.

It is a junction number, because it is equal to *n*+sod(*n*) for *n* = 294 and 303.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (307) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (5) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 49 + ... + 54.

It is an arithmetic number, because the mean of its divisors is an integer number (104).

It is an amenable number.

309 is a deficient number, since it is larger than the sum of its proper divisors (107).

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

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

The sum of its prime factors is 106.

The product of its (nonzero) digits is 27, while the sum is 12.

The square root of 309 is about 17.5783958312. The cubic root of 309 is about 6.7606143017.

Subtracting from 309 its product of nonzero digits (27), we obtain a palindrome (282).

The spelling of 309 in words is "three hundred nine", and thus it is an aban number and an oban number.

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