18645661 has 4 divisors (see below), whose sum is σ = 18654300. Its totient is φ = 18637024.

The previous prime is 18645643. The next prime is 18645673. The reversal of 18645661 is 16654681.

It is a semiprime because it is the product of two primes, and also a brilliant number, because the two primes have the same length, and also an emirpimes, since its reverse is a distinct semiprime: 16654681 = 617 ⋅26993.

It can be written as a sum of positive squares in 2 ways, for example, as 11323225 + 7322436 = 3365^2 + 2706^2 .

It is a cyclic number.

It is not a de Polignac number, because 18645661 - 2⁵ = 18645629 is a prime.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 18645661.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (18645691) by changing a digit.

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, 2025 + ... + 6433.

It is an arithmetic number, because the mean of its divisors is an integer number (4663575).

Almost surely, 2^18645661 is an apocalyptic number.

It is an amenable number.

18645661 is a deficient number, since it is larger than the sum of its proper divisors (8639).

18645661 is an equidigital number, since it uses as much as digits as its factorization.

18645661 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 8638.

The product of its digits is 34560, while the sum is 37.

The square root of 18645661 is about 4318.0621811178. The cubic root of 18645661 is about 265.1709399062.

It can be divided in two parts, 18645 and 661, that added together give a triangular number (19306 = T₁₉₆).

The spelling of 18645661 in words is "eighteen million, six hundred forty-five thousand, six hundred sixty-one".