663821 has 2 divisors, whose sum is σ = 663822. Its totient is φ = 663820.

The previous prime is 663797. The next prime is 663823. The reversal of 663821 is 128366.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 662596 + 1225 = 814^2 + 35^2 .

It is a cyclic number.

It is not a de Polignac number, because 663821 - 2¹⁰ = 662797 is a prime.

Together with 663823, it forms a pair of twin primes.

It is a Chen prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (663823) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (7) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 331910 + 331911.

It is an arithmetic number, because the mean of its divisors is an integer number (331911).

2⁶⁶³⁸²¹ is an apocalyptic number.

It is an amenable number.

663821 is a deficient number, since it is larger than the sum of its proper divisors (1).

663821 is an equidigital number, since it uses as much as digits as its factorization.

663821 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 1728, while the sum is 26.

The square root of 663821 is about 814.7521095401. The cubic root of 663821 is about 87.2335732602.

The spelling of 663821 in words is "six hundred sixty-three thousand, eight hundred twenty-one".