216705621 has 32 divisors (see below), whose sum is σ = 332928000. Its totient is φ = 124001280.

The previous prime is 216705607. The next prime is 216705679. The reversal of 216705621 is 126507612.

It is not a de Polignac number, because 216705621 - 2⁷ = 216705493 is a prime.

It is a super-2 number, since 2×216705621² = 93922652345991282, which contains 22 as substring.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (216705521) by changing a digit.

It is a polite number, since it can be written in 31 ways as a sum of consecutive naturals, for example, 361480 + ... + 362078.

It is an arithmetic number, because the mean of its divisors is an integer number (10404000).

Almost surely, 2^216705621 is an apocalyptic number.

It is an amenable number.

216705621 is a deficient number, since it is larger than the sum of its proper divisors (116222379).

216705621 is a wasteful number, since it uses less digits than its factorization.

216705621 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1209.

The product of its (nonzero) digits is 5040, while the sum is 30.

The square root of 216705621 is about 14720.9245973206. The cubic root of 216705621 is about 600.6526426164.

It can be divided in two parts, 21 and 6705621, that multiplied together give a palindrome (140818041).

The spelling of 216705621 in words is "two hundred sixteen million, seven hundred five thousand, six hundred twenty-one".