217661 has 2 divisors, whose sum is σ = 217662. Its totient is φ = 217660.

The previous prime is 217643. The next prime is 217667. The reversal of 217661 is 166712.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 184900 + 32761 = 430^2 + 181^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-217661 is a prime.

It is a Chen prime.

It is an Ulam number.

It is equal to p₁₉₄₁₈ and since 217661 and 19418 have the same sum of digits, it is a Honaker prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (217667) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 108830 + 108831.

It is an arithmetic number, because the mean of its divisors is an integer number (108831).

2²¹⁷⁶⁶¹ is an apocalyptic number.

It is an amenable number.

217661 is a deficient number, since it is larger than the sum of its proper divisors (1).

217661 is an equidigital number, since it uses as much as digits as its factorization.

217661 is an evil number, because the sum of its binary digits is even.

The product of its digits is 504, while the sum is 23.

The square root of 217661 is about 466.5415308416. The cubic root of 217661 is about 60.1534037502.

It can be divided in two parts, 217 and 661, that added together give a palindrome (878).

The spelling of 217661 in words is "two hundred seventeen thousand, six hundred sixty-one".