661657 has 4 divisors (see below), whose sum is σ = 700596. Its totient is φ = 622720.

The previous prime is 661621. The next prime is 661663. The reversal of 661657 is 756166.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 756166 = 2 ⋅378083.

It can be written as a sum of positive squares in 2 ways, for example, as 177241 + 484416 = 421^2 + 696^2 .

It is a cyclic number.

It is not a de Polignac number, because 661657 - 2¹¹ = 659609 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 not an unprimeable number, because it can be changed into a prime (661607) 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, 19444 + ... + 19477.

It is an arithmetic number, because the mean of its divisors is an integer number (175149).

2⁶⁶¹⁶⁵⁷ is an apocalyptic number.

It is an amenable number.

661657 is a deficient number, since it is larger than the sum of its proper divisors (38939).

661657 is a wasteful number, since it uses less digits than its factorization.

661657 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 38938.

The product of its digits is 7560, while the sum is 31.

The square root of 661657 is about 813.4230141814. The cubic root of 661657 is about 87.1386787262.

The spelling of 661657 in words is "six hundred sixty-one thousand, six hundred fifty-seven".