1689721 has 4 divisors (see below), whose sum is σ = 1843344. Its totient is φ = 1536100.

The previous prime is 1689719. The next prime is 1689739. The reversal of 1689721 is 1279861.

It is a happy number.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4, and also an emirpimes, since its reverse is a distinct semiprime: 1279861 = 11 ⋅116351.

It is a cyclic number.

It is not a de Polignac number, because 1689721 - 2¹ = 1689719 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (1689781) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 76795 + ... + 76816.

It is an arithmetic number, because the mean of its divisors is an integer number (460836).

2^1689721 is an apocalyptic number.

1689721 is a gapful number since it is divisible by the number (11) formed by its first and last digit.

It is an amenable number.

1689721 is a deficient number, since it is larger than the sum of its proper divisors (153623).

1689721 is a wasteful number, since it uses less digits than its factorization.

1689721 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 153622.

The product of its digits is 6048, while the sum is 34.

The square root of 1689721 is about 1299.8926878785. The cubic root of 1689721 is about 119.1072873735.

It can be divided in two parts, 168 and 9721, that added together give a palindrome (9889).

The spelling of 1689721 in words is "one million, six hundred eighty-nine thousand, seven hundred twenty-one".