216905391 has 16 divisors (see below), whose sum is σ = 323394400. Its totient is φ = 143679744.

The previous prime is 216905383. The next prime is 216905399. The reversal of 216905391 is 193509612.

It is an interprime number because it is at equal distance from previous prime (216905383) and next prime (216905399).

It is not a de Polignac number, because 216905391 - 2³ = 216905383 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (216905399) 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 15 ways as a sum of consecutive naturals, for example, 21346 + ... + 29823.

It is an arithmetic number, because the mean of its divisors is an integer number (20212150).

Almost surely, 2^216905391 is an apocalyptic number.

216905391 is a deficient number, since it is larger than the sum of its proper divisors (106489009).

216905391 is a wasteful number, since it uses less digits than its factorization.

216905391 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 51335 (or 51329 counting only the distinct ones).

The product of its (nonzero) digits is 14580, while the sum is 36.

The square root of 216905391 is about 14727.7082738626. The cubic root of 216905391 is about 600.8371564053.

The spelling of 216905391 in words is "two hundred sixteen million, nine hundred five thousand, three hundred ninety-one".