819661 has 4 divisors (see below), whose sum is σ = 841852. Its totient is φ = 797472.

The previous prime is 819659. The next prime is 819673. The reversal of 819661 is 166918.

It is a happy number.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 166918 = 2 ⋅83459.

It can be written as a sum of positive squares in 2 ways, for example, as 372100 + 447561 = 610^2 + 669^2 .

It is a cyclic number.

It is not a de Polignac number, because 819661 - 2¹ = 819659 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (819691) 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, 11040 + ... + 11113.

It is an arithmetic number, because the mean of its divisors is an integer number (210463).

2⁸¹⁹⁶⁶¹ is an apocalyptic number.

It is an amenable number.

819661 is a deficient number, since it is larger than the sum of its proper divisors (22191).

819661 is a wasteful number, since it uses less digits than its factorization.

819661 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 22190.

The product of its digits is 2592, while the sum is 31.

The square root of 819661 is about 905.3513130272. The cubic root of 819661 is about 93.5861160525.

The spelling of 819661 in words is "eight hundred nineteen thousand, six hundred sixty-one".