16561866636 has 192 divisors, whose sum is σ = 50254848000. Its totient is φ = 4619073600.

The previous prime is 16561866631. The next prime is 16561866637. The reversal of 16561866636 is 63666816561.

16561866636 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

It is a Harshad number since it is a multiple of its sum of digits (54).

It is not an unprimeable number, because it can be changed into a prime (16561866631) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 63 ways as a sum of consecutive naturals, for example, 6733975 + ... + 6736433.

It is an arithmetic number, because the mean of its divisors is an integer number (261744000).

Almost surely, 2^16561866636 is an apocalyptic number.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 16561866636, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (25127424000).

16561866636 is an abundant number, since it is smaller than the sum of its proper divisors (33692981364).

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

16561866636 is a wasteful number, since it uses less digits than its factorization.

16561866636 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2689 (or 2681 counting only the distinct ones).

The product of its digits is 5598720, while the sum is 54.

The spelling of 16561866636 in words is "sixteen billion, five hundred sixty-one million, eight hundred sixty-six thousand, six hundred thirty-six".