216635661 has 16 divisors (see below), whose sum is σ = 350118720. Its totient is φ = 131294160.

The previous prime is 216635621. The next prime is 216635693. The reversal of 216635661 is 166536612.

216635661 is a `hidden beast` number, since 2 + 16 + 635 + 6 + 6 + 1 = 666.

216635661 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

It is not a de Polignac number, because 216635661 - 2⁹ = 216635149 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (216635611) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 364410 + ... + 365003.

It is an arithmetic number, because the mean of its divisors is an integer number (21882420).

Almost surely, 2^216635661 is an apocalyptic number.

It is an amenable number.

216635661 is a deficient number, since it is larger than the sum of its proper divisors (133483059).

216635661 is a wasteful number, since it uses less digits than its factorization.

216635661 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 729433 (or 729427 counting only the distinct ones).

The product of its digits is 38880, while the sum is 36.

The square root of 216635661 is about 14718.5481960688. The cubic root of 216635661 is about 600.5879985746.

The spelling of 216635661 in words is "two hundred sixteen million, six hundred thirty-five thousand, six hundred sixty-one".