1681921 has 4 divisors (see below), whose sum is σ = 1755072. Its totient is φ = 1608772.

The previous prime is 1681907. The next prime is 1681931. The reversal of 1681921 is 1291861.

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.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-1681921 is a prime.

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 1681921.

It is not an unprimeable number, because it can be changed into a prime (1681931) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 36541 + ... + 36586.

It is an arithmetic number, because the mean of its divisors is an integer number (438768).

2^1681921 is an apocalyptic number.

It is an amenable number.

1681921 is a deficient number, since it is larger than the sum of its proper divisors (73151).

1681921 is an equidigital number, since it uses as much as digits as its factorization.

1681921 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 73150.

The product of its digits is 864, while the sum is 28.

The square root of 1681921 is about 1296.8889698043. Note that the first 3 decimals coincide. The cubic root of 1681921 is about 118.9237324074.

The spelling of 1681921 in words is "one million, six hundred eighty-one thousand, nine hundred twenty-one".