191681921 has 2 divisors, whose sum is σ = 191681922. Its totient is φ = 191681920.

The previous prime is 191681911. The next prime is 191681927. The reversal of 191681921 is 129186191.

191681921 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 123454321 + 68227600 = 11111^2 + 8260^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-191681921 is a prime.

It is a Sophie Germain prime.

It is a Chen prime.

It is a Curzon number.

It is not a weakly prime, because it can be changed into another prime (191681927) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 95840960 + 95840961.

It is an arithmetic number, because the mean of its divisors is an integer number (95840961).

Almost surely, 2^191681921 is an apocalyptic number.

It is an amenable number.

191681921 is a deficient number, since it is larger than the sum of its proper divisors (1).

191681921 is an equidigital number, since it uses as much as digits as its factorization.

191681921 is an evil number, because the sum of its binary digits is even.

The product of its digits is 7776, while the sum is 38.

The square root of 191681921 is about 13844.9240156817. The cubic root of 191681921 is about 576.5810761332.

The spelling of 191681921 in words is "one hundred ninety-one million, six hundred eighty-one thousand, nine hundred twenty-one".