216821881 has 8 divisors (see below), whose sum is σ = 218025728. Its totient is φ = 215622000.

The previous prime is 216821809. The next prime is 216821921. The reversal of 216821881 is 188128612.

It is a happy number.

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

It is a 3-Lehmer number, since φ(216821881) divides (216821881-1)³.

It is a cyclic number.

It is a Carmichael number.

It is not a de Polignac number, because 216821881 - 2¹³ = 216813689 is a prime.

It is a super-2 number, since 2×216821881² = 94023456160756322, which contains 22 as substring.

It is a deceptive number, since it divides R_216821880.

It is a self number, because there is not a number n which added to its sum of digits gives 216821881.

It is not an unprimeable number, because it can be changed into a prime (216821681) by changing a digit.

It is a Zeisel number, with parameters (1, 330).

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 218296 + ... + 219286.

It is an arithmetic number, because the mean of its divisors is an integer number (27253216).

It is a Poulet number, since it divides 2^216821880-1.

Almost surely, 2^216821881 is an apocalyptic number.

It is an amenable number.

216821881 is a deficient number, since it is larger than the sum of its proper divisors (1203847).

216821881 is an equidigital number, since it uses as much as digits as its factorization.

216821881 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1983.

The product of its digits is 12288, while the sum is 37.

The square root of 216821881 is about 14724.8728687211. The cubic root of 216821881 is about 600.7600377571.

The spelling of 216821881 in words is "two hundred sixteen million, eight hundred twenty-one thousand, eight hundred eighty-one".