661709 has 4 divisors (see below), whose sum is σ = 666300. Its totient is φ = 657120.

The previous prime is 661697. The next prime is 661721. The reversal of 661709 is 907166.

It is a happy number.

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

It is an interprime number because it is at equal distance from previous prime (661697) and next prime (661721).

It can be written as a sum of positive squares in 2 ways, for example, as 157609 + 504100 = 397^2 + 710^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-661709 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 (661769) 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, 2072 + ... + 2369.

It is an arithmetic number, because the mean of its divisors is an integer number (166575).

2⁶⁶¹⁷⁰⁹ is an apocalyptic number.

It is an amenable number.

661709 is a deficient number, since it is larger than the sum of its proper divisors (4591).

661709 is a wasteful number, since it uses less digits than its factorization.

661709 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 4590.

The product of its (nonzero) digits is 2268, while the sum is 29.

The square root of 661709 is about 813.4549772421. The cubic root of 661709 is about 87.1409614259.

The spelling of 661709 in words is "six hundred sixty-one thousand, seven hundred nine".