216561221217 has 32 divisors (see below), whose sum is σ = 352552728960. Its totient is φ = 130291176960.

The previous prime is 216561221213. The next prime is 216561221221. The reversal of 216561221217 is 712122165612.

216561221217 is a `hidden beast` number, since 2 + 1 + 6 + 5 + 612 + 21 + 2 + 17 = 666.

It is an interprime number because it is at equal distance from previous prime (216561221213) and next prime (216561221221).

It is not a de Polignac number, because 216561221217 - 2² = 216561221213 is a prime.

It is a super-2 number, since 2×216561221217² (a number of 23 digits) contains 22 as substring.

It is not an unprimeable number, because it can be changed into a prime (216561221213) 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, 2620488 + ... + 2701865.

It is an arithmetic number, because the mean of its divisors is an integer number (11017272780).

Almost surely, 2^216561221217 is an apocalyptic number.

216561221217 is a gapful number since it is divisible by the number (27) formed by its first and last digit.

It is an amenable number.

216561221217 is a deficient number, since it is larger than the sum of its proper divisors (135991507743).

216561221217 is a wasteful number, since it uses less digits than its factorization.

216561221217 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 5322510 (or 5322504 counting only the distinct ones).

The product of its digits is 20160, while the sum is 36.

Adding to 216561221217 its reverse (712122165612), we get a palindrome (928683386829).

The spelling of 216561221217 in words is "two hundred sixteen billion, five hundred sixty-one million, two hundred twenty-one thousand, two hundred seventeen".