16561818 has 48 divisors (see below), whose sum is σ = 44169216. Its totient is φ = 4367520.

The previous prime is 16561799. The next prime is 16561819. The reversal of 16561818 is 81816561.

16561818 is a `hidden beast` number, since 16 + 561 + 81 + 8 = 666.

It is an alternating number because its digits alternate between odd and even.

16561818 is a modest number, since divided by 1818 gives 1656 as remainder.

It is a Curzon number.

It is not an unprimeable number, because it can be changed into a prime (16561819) by changing a digit.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 3418 + ... + 6693.

It is an arithmetic number, because the mean of its divisors is an integer number (920192).

Almost surely, 2^16561818 is an apocalyptic number.

16561818 is a gapful number since it is divisible by the number (18) formed by its first and last digit.

16561818 is an abundant number, since it is smaller than the sum of its proper divisors (27607398).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

16561818 is a wasteful number, since it uses less digits than its factorization.

16561818 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 10139 (or 10136 counting only the distinct ones).

The product of its digits is 11520, while the sum is 36.

The square root of 16561818 is about 4069.6213583084. The cubic root of 16561818 is about 254.8997068106.

The spelling of 16561818 in words is "sixteen million, five hundred sixty-one thousand, eight hundred eighteen".