661729 has 4 divisors (see below), whose sum is σ = 663984. Its totient is φ = 659476.

The previous prime is 661721. The next prime is 661741. The reversal of 661729 is 927166.

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 661729 - 2³ = 661721 is a prime.

It is a Smith number, since the sum of its digits (31) coincides with the sum of the digits of its prime factors. Since it is squarefree, it is also a hoax number.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 661729.

It is not an unprimeable number, because it can be changed into a prime (661721) 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, 607 + ... + 1300.

It is an arithmetic number, because the mean of its divisors is an integer number (165996).

2⁶⁶¹⁷²⁹ is an apocalyptic number.

It is an amenable number.

661729 is a deficient number, since it is larger than the sum of its proper divisors (2255).

661729 is a wasteful number, since it uses less digits than its factorization.

661729 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2254.

The product of its digits is 4536, while the sum is 31.

The square root of 661729 is about 813.4672703926. The cubic root of 661729 is about 87.1418393554.

The spelling of 661729 in words is "six hundred sixty-one thousand, seven hundred twenty-nine".