391683681 has 21 divisors (see below), whose sum is σ = 588059139. Its totient is φ = 260766216.

The previous prime is 391683679. The next prime is 391683703. The reversal of 391683681 is 186386193.

It is a happy number.

The square root of 391683681 is 19791.

It is a perfect power (a square), and thus also a powerful number.

It can be written as a sum of positive squares in only one way, i.e., 383180625 + 8503056 = 19575^2 + 2916^2 .

It is not a de Polignac number, because 391683681 - 2¹ = 391683679 is a prime.

It is a super-2 number, since 2×391683681² = 306832211923419522, which contains 22 as substring.

It is not an unprimeable number, because it can be changed into a prime (391683671) by changing a digit.

It is a polite number, since it can be written in 20 ways as a sum of consecutive naturals, for example, 533991 + ... + 534723.

Almost surely, 2^391683681 is an apocalyptic number.

391683681 is the 19791-st square number.

391683681 is the 9896-th centered octagonal number.

It is an amenable number.

391683681 is a deficient number, since it is larger than the sum of its proper divisors (196375458).

391683681 is an frugal number, since it uses more digits than its factorization.

391683681 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1484 (or 736 counting only the distinct ones).

The product of its digits is 186624, while the sum is 45.

The cubic root of 391683681 is about 731.6642339421.

Multiplying 391683681 by its product of digits (186624), we get a square (73097575282944 = 8549712²).

It can be divided in two parts, 39168 and 3681, that added together give a square (42849 = 207²).

The spelling of 391683681 in words is "three hundred ninety-one million, six hundred eighty-three thousand, six hundred eighty-one".