16681991 has 2 divisors, whose sum is σ = 16681992. Its totient is φ = 16681990.

The previous prime is 16681949. The next prime is 16681993. The reversal of 16681991 is 19918661.

It is a happy number.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 16681991 - 2⁶ = 16681927 is a prime.

It is a Sophie Germain prime.

Together with 16681993, it forms a pair of twin primes.

It is a Chen prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (16681993) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 8340995 + 8340996.

It is an arithmetic number, because the mean of its divisors is an integer number (8340996).

Almost surely, 2^16681991 is an apocalyptic number.

16681991 is a deficient number, since it is larger than the sum of its proper divisors (1).

16681991 is an equidigital number, since it uses as much as digits as its factorization.

16681991 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 23328, while the sum is 41.

The square root of 16681991 is about 4084.3593132828. The cubic root of 16681991 is about 255.5147413571.

The spelling of 16681991 in words is "sixteen million, six hundred eighty-one thousand, nine hundred ninety-one".