1687681 has 4 divisors (see below), whose sum is σ = 1733332. Its totient is φ = 1642032.

The previous prime is 1687669. The next prime is 1687729. The reversal of 1687681 is 1867861.

1687681 = 113² + 114² + ... + 186².

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 705600 + 982081 = 840^2 + 991^2 .

It is a cyclic number.

It is not a de Polignac number, because 1687681 - 2¹⁷ = 1556609 is a prime.

It is a super-2 number, since 2×1687681² = 5696534315522, which contains 22 as substring.

It is a Harshad number since it is a multiple of its sum of digits (37), and also a Moran number because the ratio is a prime number: 45613 = 1687681 / (1 + 6 + 8 + 7 + 6 + 8 + 1).

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 1687681.

It is not an unprimeable number, because it can be changed into a prime (1687661) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (7) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 22770 + ... + 22843.

It is an arithmetic number, because the mean of its divisors is an integer number (433333).

2^1687681 is an apocalyptic number.

It is an amenable number.

1687681 is a deficient number, since it is larger than the sum of its proper divisors (45651).

1687681 is an equidigital number, since it uses as much as digits as its factorization.

1687681 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 45650.

The product of its digits is 16128, while the sum is 37.

The square root of 1687681 is about 1299.1077707411. The cubic root of 1687681 is about 119.0593353320.

The spelling of 1687681 in words is "one million, six hundred eighty-seven thousand, six hundred eighty-one".