663921 has 12 divisors (see below), whose sum is σ = 973440. Its totient is φ = 435960.

The previous prime is 663907. The next prime is 663937. The reversal of 663921 is 129366.

It is a happy number.

663921 is a `hidden beast` number, since 6 + 639 + 21 = 666.

It is not a de Polignac number, because 663921 - 2⁶ = 663857 is a prime.

It is a Smith number, since the sum of its digits (27) coincides with the sum of the digits of its prime factors.

It is not an unprimeable number, because it can be changed into a prime (663961) by changing a digit.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 120 + ... + 1158.

It is an arithmetic number, because the mean of its divisors is an integer number (81120).

2⁶⁶³⁹²¹ is an apocalyptic number.

It is an amenable number.

663921 is a deficient number, since it is larger than the sum of its proper divisors (309519).

663921 is a wasteful number, since it uses less digits than its factorization.

663921 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1116 (or 1113 counting only the distinct ones).

The product of its digits is 1944, while the sum is 27.

The square root of 663921 is about 814.8134755881. The cubic root of 663921 is about 87.2379534165.

The spelling of 663921 in words is "six hundred sixty-three thousand, nine hundred twenty-one".