216561969 has 24 divisors (see below), whose sum is σ = 337569960. Its totient is φ = 132993792.

The previous prime is 216561953. The next prime is 216561971. The reversal of 216561969 is 969165612.

It is a happy number.

216561969 is a `hidden beast` number, since 21 + 6 + 5 + 619 + 6 + 9 = 666.

216561969 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

It can be written as a sum of positive squares in 4 ways, for example, as 28515600 + 188046369 = 5340^2 + 13713^2 .

It is not a de Polignac number, because 216561969 - 2⁴ = 216561953 is a prime.

It is a super-2 number, since 2×216561969² = 93798172834313922, which contains 22 as substring.

It is a Curzon number.

It is not an unprimeable number, because it can be changed into a prime (216561769) 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, 64947 + ... + 68199.

It is an arithmetic number, because the mean of its divisors is an integer number (14065415).

Almost surely, 2^216561969 is an apocalyptic number.

It is an amenable number.

216561969 is a deficient number, since it is larger than the sum of its proper divisors (121007991).

216561969 is a wasteful number, since it uses less digits than its factorization.

216561969 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 3841 (or 3838 counting only the distinct ones).

The product of its digits is 174960, while the sum is 45.

The square root of 216561969 is about 14716.0446112398. The cubic root of 216561969 is about 600.5198910587.

The spelling of 216561969 in words is "two hundred sixteen million, five hundred sixty-one thousand, nine hundred sixty-nine".