16561665 has 48 divisors (see below), whose sum is σ = 30558528. Its totient is φ = 8600256.

The previous prime is 16561661. The next prime is 16561667. The reversal of 16561665 is 56616561.

16561665 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

It is not a de Polignac number, because 16561665 - 2² = 16561661 is a prime.

It is not an unprimeable number, because it can be changed into a prime (16561661) by changing a digit.

It is a polite number, since it can be written in 47 ways as a sum of consecutive naturals, for example, 52087 + ... + 52403.

It is an arithmetic number, because the mean of its divisors is an integer number (636636).

Almost surely, 2^16561665 is an apocalyptic number.

16561665 is a gapful number since it is divisible by the number (15) formed by its first and last digit.

It is an amenable number.

16561665 is a deficient number, since it is larger than the sum of its proper divisors (13996863).

16561665 is an equidigital number, since it uses as much as digits as its factorization.

16561665 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 380 (or 368 counting only the distinct ones).

The product of its digits is 32400, while the sum is 36.

The square root of 16561665 is about 4069.6025604474. The cubic root of 16561665 is about 254.8989218772.

It can be divided in two parts, 1656 and 1665, that added together give a triangular number (3321 = T₈₁).

The spelling of 16561665 in words is "sixteen million, five hundred sixty-one thousand, six hundred sixty-five".