216805561 has 8 divisors (see below), whose sum is σ = 260818880. Its totient is φ = 176052528.

The previous prime is 216805541. The next prime is 216805571. The reversal of 216805561 is 165508612.

It is a happy number.

216805561 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is not a de Polignac number, because 216805561 - 2¹¹ = 216803513 is a prime.

It is not an unprimeable number, because it can be changed into a prime (216805531) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 814926 + ... + 815191.

It is an arithmetic number, because the mean of its divisors is an integer number (32602360).

Almost surely, 2^216805561 is an apocalyptic number.

It is an amenable number.

216805561 is a deficient number, since it is larger than the sum of its proper divisors (44013319).

216805561 is a wasteful number, since it uses less digits than its factorization.

216805561 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1630143.

The product of its (nonzero) digits is 14400, while the sum is 34.

The square root of 216805561 is about 14724.3186939159. The cubic root of 216805561 is about 600.7449644785.

The spelling of 216805561 in words is "two hundred sixteen million, eight hundred five thousand, five hundred sixty-one".