391661 has 2 divisors, whose sum is σ = 391662. Its totient is φ = 391660.

The previous prime is 391639. The next prime is 391679. The reversal of 391661 is 166193.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 354025 + 37636 = 595^2 + 194^2 .

It is a cyclic number.

It is not a de Polignac number, because 391661 - 2¹⁸ = 129517 is a prime.

It is a Sophie Germain prime.

It is a Chen prime.

It is a Curzon number.

It is a self number, because there is not a number n which added to its sum of digits gives 391661.

It is a congruent number.

It is an inconsummate number, since it does not exist a number n which divided by its sum of digits gives 391661.

It is not a weakly prime, because it can be changed into another prime (391631) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 195830 + 195831.

It is an arithmetic number, because the mean of its divisors is an integer number (195831).

2³⁹¹⁶⁶¹ is an apocalyptic number.

It is an amenable number.

391661 is a deficient number, since it is larger than the sum of its proper divisors (1).

391661 is an equidigital number, since it uses as much as digits as its factorization.

391661 is an evil number, because the sum of its binary digits is even.

The product of its digits is 972, while the sum is 26.

The square root of 391661 is about 625.8282512000. The cubic root of 391661 is about 73.1650110984.

The spelling of 391661 in words is "three hundred ninety-one thousand, six hundred sixty-one".