1691721 has 12 divisors (see below), whose sum is σ = 2587572. Its totient is φ = 1061376.

The previous prime is 1691693. The next prime is 1691737. The reversal of 1691721 is 1271961.

It can be written as a sum of positive squares in 2 ways, for example, as 810000 + 881721 = 900^2 + 939^2 .

It is not a de Polignac number, because 1691721 - 2⁵ = 1691689 is a prime.

It is not an unprimeable number, because it can be changed into a prime (1691771) 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, 5376 + ... + 5681.

It is an arithmetic number, because the mean of its divisors is an integer number (215631).

2^1691721 is an apocalyptic number.

It is an amenable number.

1691721 is a deficient number, since it is larger than the sum of its proper divisors (895851).

1691721 is a wasteful number, since it uses less digits than its factorization.

1691721 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 11080 (or 11077 counting only the distinct ones).

The product of its digits is 756, while the sum is 27.

The square root of 1691721 is about 1300.6617546465. The cubic root of 1691721 is about 119.1542617262.

The spelling of 1691721 in words is "one million, six hundred ninety-one thousand, seven hundred twenty-one".