217561 has 2 divisors, whose sum is σ = 217562. Its totient is φ = 217560.

The previous prime is 217559. The next prime is 217573. The reversal of 217561 is 165712.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 118336 + 99225 = 344^2 + 315^2 .

It is a cyclic number.

It is not a de Polignac number, because 217561 - 2¹ = 217559 is a prime.

Together with 217559, it forms a pair of twin primes.

217561 is a lucky number.

It is not a weakly prime, because it can be changed into another prime (217361) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 108780 + 108781.

It is an arithmetic number, because the mean of its divisors is an integer number (108781).

2²¹⁷⁵⁶¹ is an apocalyptic number.

It is an amenable number.

217561 is a deficient number, since it is larger than the sum of its proper divisors (1).

217561 is an equidigital number, since it uses as much as digits as its factorization.

217561 is an evil number, because the sum of its binary digits is even.

The product of its digits is 420, while the sum is 22.

The square root of 217561 is about 466.4343469343. The cubic root of 217561 is about 60.1441902457.

The spelling of 217561 in words is "two hundred seventeen thousand, five hundred sixty-one".