661806 has 12 divisors (see below), whose sum is σ = 1433952. Its totient is φ = 220596.

The previous prime is 661777. The next prime is 661823. The reversal of 661806 is 608166.

It is a self number, because there is not a number n which added to its sum of digits gives 661806.

It is a congruent number.

It is an inconsummate number, since it does not exist a number n which divided by its sum of digits gives 661806.

It is an unprimeable number.

661806 is an untouchable number, because it is not equal to the sum of proper divisors of any number.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 18366 + ... + 18401.

It is an arithmetic number, because the mean of its divisors is an integer number (119496).

2⁶⁶¹⁸⁰⁶ is an apocalyptic number.

661806 is an abundant number, since it is smaller than the sum of its proper divisors (772146).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

661806 is a wasteful number, since it uses less digits than its factorization.

661806 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 36775 (or 36772 counting only the distinct ones).

The product of its (nonzero) digits is 1728, while the sum is 27.

The square root of 661806 is about 813.5145972876. The cubic root of 661806 is about 87.1452192191.

The spelling of 661806 in words is "six hundred sixty-one thousand, eight hundred six".