6541555991 has 2 divisors, whose sum is σ = 6541555992. Its totient is φ = 6541555990.

The previous prime is 6541555963. The next prime is 6541556033. The reversal of 6541555991 is 1995551456.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 6541555991 - 2¹⁴ = 6541539607 is a prime.

It is a Sophie Germain prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (6541555931) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 3270777995 + 3270777996.

It is an arithmetic number, because the mean of its divisors is an integer number (3270777996).

Almost surely, 2^6541555991 is an apocalyptic number.

6541555991 is a deficient number, since it is larger than the sum of its proper divisors (1).

6541555991 is an equidigital number, since it uses as much as digits as its factorization.

6541555991 is an evil number, because the sum of its binary digits is even.

The product of its digits is 1215000, while the sum is 50.

The square root of 6541555991 is about 80879.8861955184. The cubic root of 6541555991 is about 1870.2242661435.

The spelling of 6541555991 in words is "six billion, five hundred forty-one million, five hundred fifty-five thousand, nine hundred ninety-one".