671821 has 6 divisors (see below), whose sum is σ = 709422. Its totient is φ = 636120.

The previous prime is 671791. The next prime is 671831. The reversal of 671821 is 128176.

It can be written as a sum of positive squares in only one way, i.e., 346921 + 324900 = 589^2 + 570^2 .

It is not a de Polignac number, because 671821 - 2¹⁵ = 639053 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (671831) 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 5 ways as a sum of consecutive naturals, for example, 570 + ... + 1291.

It is an arithmetic number, because the mean of its divisors is an integer number (118237).

2⁶⁷¹⁸²¹ is an apocalyptic number.

It is an amenable number.

671821 is a deficient number, since it is larger than the sum of its proper divisors (37601).

671821 is a wasteful number, since it uses less digits than its factorization.

671821 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1899 (or 1880 counting only the distinct ones).

The product of its digits is 672, while the sum is 25.

The square root of 671821 is about 819.6468751847. The cubic root of 671821 is about 87.5826049848.

Adding to 671821 its reverse (128176), we get a palindrome (799997).

The spelling of 671821 in words is "six hundred seventy-one thousand, eight hundred twenty-one".