816661 has 4 divisors (see below), whose sum is σ = 852192. Its totient is φ = 781132.

The previous prime is 816653. The next prime is 816667. The reversal of 816661 is 166618.

816661 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

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 not a de Polignac number, because 816661 - 2³ = 816653 is a prime.

It is a Duffinian number.

816661 is a lucky number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (816667) 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, 17731 + ... + 17776.

It is an arithmetic number, because the mean of its divisors is an integer number (213048).

2⁸¹⁶⁶⁶¹ is an apocalyptic number.

It is an amenable number.

816661 is a deficient number, since it is larger than the sum of its proper divisors (35531).

816661 is a wasteful number, since it uses less digits than its factorization.

816661 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 35530.

The product of its digits is 1728, while the sum is 28.

The square root of 816661 is about 903.6929788374. The cubic root of 816661 is about 93.4717998591.

The spelling of 816661 in words is "eight hundred sixteen thousand, six hundred sixty-one".