216921817 has 4 divisors (see below), whose sum is σ = 247910656. Its totient is φ = 185932980.

The previous prime is 216921791. The next prime is 216921829. The reversal of 216921817 is 718129612.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is not a de Polignac number, because 216921817 - 2¹⁹ = 216397529 is a prime.

It is not an unprimeable number, because it can be changed into a prime (216921317) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (19) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 15494409 + ... + 15494422.

It is an arithmetic number, because the mean of its divisors is an integer number (61977664).

Almost surely, 2^216921817 is an apocalyptic number.

It is an amenable number.

216921817 is a deficient number, since it is larger than the sum of its proper divisors (30988839).

216921817 is an equidigital number, since it uses as much as digits as its factorization.

216921817 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 30988838.

The product of its digits is 12096, while the sum is 37.

The square root of 216921817 is about 14728.2659196526. The cubic root of 216921817 is about 600.8523229287.

The spelling of 216921817 in words is "two hundred sixteen million, nine hundred twenty-one thousand, eight hundred seventeen".