1663645 has 4 divisors (see below), whose sum is σ = 1996380. Its totient is φ = 1330912.

The previous prime is 1663619. The next prime is 1663681. The reversal of 1663645 is 5463661.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 5463661 = 7 ⋅780523.

It can be written as a sum of positive squares in 2 ways, for example, as 257049 + 1406596 = 507^2 + 1186^2 .

It is a cyclic number.

It is not a de Polignac number, because 1663645 - 2⁷ = 1663517 is a prime.

It is a Smith number, since the sum of its digits (31) coincides with the sum of the digits of its prime factors. Since it is squarefree, it is also a hoax number.

It is a congruent number.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 166360 + ... + 166369.

It is an arithmetic number, because the mean of its divisors is an integer number (499095).

2^1663645 is an apocalyptic number.

It is an amenable number.

1663645 is a deficient number, since it is larger than the sum of its proper divisors (332735).

1663645 is an equidigital number, since it uses as much as digits as its factorization.

1663645 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 332734.

The product of its digits is 12960, while the sum is 31.

The square root of 1663645 is about 1289.8236313543. The cubic root of 1663645 is about 118.4914151650.

The spelling of 1663645 in words is "one million, six hundred sixty-three thousand, six hundred forty-five".