821609 has 4 divisors (see below), whose sum is σ = 835140. Its totient is φ = 808080.

The previous prime is 821603. The next prime is 821641. The reversal of 821609 is 906128.

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 225625 + 595984 = 475^2 + 772^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-821609 is a prime.

It is a Duffinian number.

It is a Curzon number.

It is a plaindrome in base 15.

It is not an unprimeable number, because it can be changed into a prime (821603) 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, 6674 + ... + 6795.

It is an arithmetic number, because the mean of its divisors is an integer number (208785).

2⁸²¹⁶⁰⁹ is an apocalyptic number.

It is an amenable number.

821609 is a deficient number, since it is larger than the sum of its proper divisors (13531).

821609 is a wasteful number, since it uses less digits than its factorization.

821609 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 13530.

The product of its (nonzero) digits is 864, while the sum is 26.

The square root of 821609 is about 906.4265000539. The cubic root of 821609 is about 93.6601960776.

The spelling of 821609 in words is "eight hundred twenty-one thousand, six hundred nine".