161621720217 has 12 divisors (see below), whose sum is σ = 237280704804. Its totient is φ = 105981455520.

The previous prime is 161621720201. The next prime is 161621720263. The reversal of 161621720217 is 712027126161.

161621720217 is a `hidden beast` number, since 1 + 6 + 1 + 621 + 7 + 2 + 0 + 21 + 7 = 666.

It can be written as a sum of positive squares in 2 ways, for example, as 80767366416 + 80854353801 = 284196^2 + 284349^2 .

It is not a de Polignac number, because 161621720217 - 2⁴ = 161621720201 is a prime.

It is a super-2 number, since 2×161621720217² (a number of 23 digits) contains 22 as substring.

It is not an unprimeable number, because it can be changed into a prime (161621720297) by changing a digit.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 147195918 + ... + 147197015.

It is an arithmetic number, because the mean of its divisors is an integer number (19773392067).

Almost surely, 2^161621720217 is an apocalyptic number.

It is an amenable number.

161621720217 is a deficient number, since it is larger than the sum of its proper divisors (75658984587).

161621720217 is a wasteful number, since it uses less digits than its factorization.

161621720217 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 294393000 (or 294392997 counting only the distinct ones).

The product of its (nonzero) digits is 14112, while the sum is 36.

Adding to 161621720217 its reverse (712027126161), we get a palindrome (873648846378).

The spelling of 161621720217 in words is "one hundred sixty-one billion, six hundred twenty-one million, seven hundred twenty thousand, two hundred seventeen".