657661 has 2 divisors, whose sum is σ = 657662. Its totient is φ = 657660.

The previous prime is 657659. The next prime is 657703. The reversal of 657661 is 166756.

657661 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 630436 + 27225 = 794^2 + 165^2 .

It is a cyclic number.

It is not a de Polignac number, because 657661 - 2¹ = 657659 is a prime.

Together with 657659, it forms a pair of twin primes.

It is an Ulam number.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (657061) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 328830 + 328831.

It is an arithmetic number, because the mean of its divisors is an integer number (328831).

2⁶⁵⁷⁶⁶¹ is an apocalyptic number.

It is an amenable number.

657661 is a deficient number, since it is larger than the sum of its proper divisors (1).

657661 is an equidigital number, since it uses as much as digits as its factorization.

657661 is an evil number, because the sum of its binary digits is even.

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

The square root of 657661 is about 810.9630077877. The cubic root of 657661 is about 86.9629031078.

The spelling of 657661 in words is "six hundred fifty-seven thousand, six hundred sixty-one".