309681 has 12 divisors (see below), whose sum is σ = 471120. Its totient is φ = 195480.

The previous prime is 309677. The next prime is 309707. The reversal of 309681 is 186903.

It is not a de Polignac number, because 309681 - 2² = 309677 is a prime.

It is a super-2 number, since 2×309681² = 191804643522, which contains 22 as substring.

It is a Smith number, since the sum of its digits (27) coincides with the sum of the digits of its prime factors.

It is a Curzon number.

309681 is a lucky number.

It is an inconsummate number, since it does not exist a number n which divided by its sum of digits gives 309681.

It is not an unprimeable number, because it can be changed into a prime (309671) 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, 735 + ... + 1076.

It is an arithmetic number, because the mean of its divisors is an integer number (39260).

2³⁰⁹⁶⁸¹ is an apocalyptic number.

It is an amenable number.

309681 is a deficient number, since it is larger than the sum of its proper divisors (161439).

309681 is a wasteful number, since it uses less digits than its factorization.

309681 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1836 (or 1833 counting only the distinct ones).

The product of its (nonzero) digits is 1296, while the sum is 27.

The square root of 309681 is about 556.4898920915. The cubic root of 309681 is about 67.6557719308.

It can be divided in two parts, 309 and 681, that added together give a triangular number (990 = T₄₄).

The spelling of 309681 in words is "three hundred nine thousand, six hundred eighty-one".