216821540881 has 9 divisors (see below), whose sum is σ = 238330133769. Its totient is φ = 197105835300.

The previous prime is 216821540861. The next prime is 216821540909. The reversal of 216821540881 is 188045128612.

It is a happy number.

The square root of 216821540881 is 465641.

It is a perfect power (a square), and thus also a powerful number.

It is not a de Polignac number, because 216821540881 - 2¹¹ = 216821538833 is a prime.

It is a super-2 number, since 2×216821540881² (a number of 23 digits) contains 22 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (216821540861) by changing a digit.

It is a polite number, since it can be written in 8 ways as a sum of consecutive naturals, for example, 5100886 + ... + 5143216.

Almost surely, 2^216821540881 is an apocalyptic number.

216821540881 is the 465641-st square number.

216821540881 is the 232821-st centered octagonal number.

It is an amenable number.

216821540881 is a deficient number, since it is larger than the sum of its proper divisors (21508592888).

216821540881 is an frugal number, since it uses more digits than its factorization.

216821540881 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 84684 (or 42342 counting only the distinct ones).

The product of its (nonzero) digits is 245760, while the sum is 46.

The spelling of 216821540881 in words is "two hundred sixteen billion, eight hundred twenty-one million, five hundred forty thousand, eight hundred eighty-one".