206541991 has 2 divisors, whose sum is σ = 206541992. Its totient is φ = 206541990.

The previous prime is 206541983. The next prime is 206541997. The reversal of 206541991 is 199145602.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 206541991 - 2³ = 206541983 is a prime.

It is a self number, because there is not a number n which added to its sum of digits gives 206541991.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (206541997) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 103270995 + 103270996.

It is an arithmetic number, because the mean of its divisors is an integer number (103270996).

Almost surely, 2^206541991 is an apocalyptic number.

206541991 is a deficient number, since it is larger than the sum of its proper divisors (1).

206541991 is an equidigital number, since it uses as much as digits as its factorization.

206541991 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 19440, while the sum is 37.

The square root of 206541991 is about 14371.5688426838. The cubic root of 206541991 is about 591.1115605413. Note that the first 3 decimals are identical.

It can be divided in two parts, 20654 and 1991, that multiplied together give a palindrome (41122114).

The spelling of 206541991 in words is "two hundred six million, five hundred forty-one thousand, nine hundred ninety-one".