684161981 has 4 divisors (see below), whose sum is σ = 690935964. Its totient is φ = 677388000.

The previous prime is 684161977. The next prime is 684161987. The reversal of 684161981 is 189161486.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 432432025 + 251729956 = 20795^2 + 15866^2 .

It is a cyclic number.

It is not a de Polignac number, because 684161981 - 2² = 684161977 is a prime.

It is a super-2 number, since 2×684161981² = 936155232491688722, which contains 22 as substring.

It is a Duffinian number.

It is a Curzon number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (684161987) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (19) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 3386840 + ... + 3387041.

It is an arithmetic number, because the mean of its divisors is an integer number (172733991).

Almost surely, 2^684161981 is an apocalyptic number.

It is an amenable number.

684161981 is a deficient number, since it is larger than the sum of its proper divisors (6773983).

684161981 is a wasteful number, since it uses less digits than its factorization.

684161981 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 6773982.

The product of its digits is 82944, while the sum is 44.

The square root of 684161981 is about 26156.4902270928. The cubic root of 684161981 is about 881.1563573284.

The spelling of 684161981 in words is "six hundred eighty-four million, one hundred sixty-one thousand, nine hundred eighty-one".