216208781 has 4 divisors (see below), whose sum is σ = 218349564. Its totient is φ = 214068000.

The previous prime is 216208777. The next prime is 216208807. The reversal of 216208781 is 187802612.

216208781 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 199967881 + 16240900 = 14141^2 + 4030^2 .

It is a cyclic number.

It is not a de Polignac number, because 216208781 - 2² = 216208777 is a prime.

It is a super-2 number, since 2×216208781² = 93492473963011922, which contains 22 as substring.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (216208711) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 1070240 + ... + 1070441.

It is an arithmetic number, because the mean of its divisors is an integer number (54587391).

Almost surely, 2^216208781 is an apocalyptic number.

It is an amenable number.

216208781 is a deficient number, since it is larger than the sum of its proper divisors (2140783).

216208781 is a wasteful number, since it uses less digits than its factorization.

216208781 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2140782.

The product of its (nonzero) digits is 10752, while the sum is 35.

The square root of 216208781 is about 14704.0396150174. The cubic root of 216208781 is about 600.1932534892.

The spelling of 216208781 in words is "two hundred sixteen million, two hundred eight thousand, seven hundred eighty-one".