16561216 has 42 divisors (see below), whose sum is σ = 38236398. Its totient is φ = 7096320.

The previous prime is 16561211. The next prime is 16561243. The reversal of 16561216 is 61216561.

It can be written as a sum of positive squares in only one way, i.e., 11289600 + 5271616 = 3360^2 + 2296^2 .

It is a Harshad number since it is a multiple of its sum of digits (28).

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

It is a nialpdrome in base 16.

It is not an unprimeable number, because it can be changed into a prime (16561211) 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 5 ways as a sum of consecutive naturals, for example, 496 + ... + 5776.

Almost surely, 2^16561216 is an apocalyptic number.

16561216 is a gapful number since it is divisible by the number (16) formed by its first and last digit.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 16561216, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (19118199).

16561216 is an abundant number, since it is smaller than the sum of its proper divisors (21675182).

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

16561216 is an equidigital number, since it uses as much as digits as its factorization.

16561216 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 5307 (or 5290 counting only the distinct ones).

The product of its digits is 2160, while the sum is 28.

The square root of 16561216 is about 4069.5473949814. The cubic root of 16561216 is about 254.8966183517.

Adding to 16561216 its reverse (61216561), we get a palindrome (77777777).

The spelling of 16561216 in words is "sixteen million, five hundred sixty-one thousand, two hundred sixteen".