217661231 has 2 divisors, whose sum is σ = 217661232. Its totient is φ = 217661230.

The previous prime is 217661209. The next prime is 217661233. The reversal of 217661231 is 132166712.

It is a strong prime.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-217661231 is a prime.

It is a super-2 number, since 2×217661231² = 94752822960870722, which contains 22 as substring.

It is a Sophie Germain prime.

Together with 217661233, it forms a pair of twin primes.

It is a Chen prime.

It is a junction number, because it is equal to n+sod(n) for n = 217661194 and 217661203.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (217661233) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (19) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 108830615 + 108830616.

It is an arithmetic number, because the mean of its divisors is an integer number (108830616).

Almost surely, 2^217661231 is an apocalyptic number.

217661231 is a deficient number, since it is larger than the sum of its proper divisors (1).

217661231 is an equidigital number, since it uses as much as digits as its factorization.

217661231 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 3024, while the sum is 29.

The square root of 217661231 is about 14753.3464339451. The cubic root of 217661231 is about 601.5342503012.

The spelling of 217661231 in words is "two hundred seventeen million, six hundred sixty-one thousand, two hundred thirty-one".