661699 has 4 divisors (see below), whose sum is σ = 677880. Its totient is φ = 645520.

The previous prime is 661697. The next prime is 661721. The reversal of 661699 is 996166.

It is a semiprime because it is the product of two primes.

It is a cyclic number.

It is not a de Polignac number, because 661699 - 2¹ = 661697 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (661697) 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, 8029 + ... + 8110.

It is an arithmetic number, because the mean of its divisors is an integer number (169470).

2⁶⁶¹⁶⁹⁹ is an apocalyptic number.

661699 is a deficient number, since it is larger than the sum of its proper divisors (16181).

661699 is a wasteful number, since it uses less digits than its factorization.

661699 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 16180.

The product of its digits is 17496, while the sum is 37.

The square root of 661699 is about 813.4488305972. The cubic root of 661699 is about 87.1405224544.

Adding to 661699 its product of digits (17496), we get a triangular number (679195 = T₁₁₆₅).

The spelling of 661699 in words is "six hundred sixty-one thousand, six hundred ninety-nine".