663661 has 2 divisors, whose sum is σ = 663662. Its totient is φ = 663660.

The previous prime is 663659. The next prime is 663683. The reversal of 663661 is 166366.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 570025 + 93636 = 755^2 + 306^2 .

It is a cyclic number.

It is not a de Polignac number, because 663661 - 2¹ = 663659 is a prime.

Together with 663659, it forms a pair of twin primes.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (663601) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 331830 + 331831.

It is an arithmetic number, because the mean of its divisors is an integer number (331831).

2⁶⁶³⁶⁶¹ is an apocalyptic number.

It is an amenable number.

663661 is a deficient number, since it is larger than the sum of its proper divisors (1).

663661 is an equidigital number, since it uses as much as digits as its factorization.

663661 is an evil number, because the sum of its binary digits is even.

The product of its digits is 3888, while the sum is 28.

The square root of 663661 is about 814.6539142483. The cubic root of 663661 is about 87.2265640949.

The spelling of 663661 in words is "six hundred sixty-three thousand, six hundred sixty-one".