21991511185439 has 2 divisors, whose sum is σ = 21991511185440. Its totient is φ = 21991511185438.

The previous prime is 21991511185363. The next prime is 21991511185447. The reversal of 21991511185439 is 93458111519912.

It is a happy number.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 21991511185439 - 2⁸ = 21991511185183 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21991511185339) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10995755592719 + 10995755592720.

It is an arithmetic number, because the mean of its divisors is an integer number (10995755592720).

Almost surely, 2^{21991511185439} is an apocalyptic number.

21991511185439 is a deficient number, since it is larger than the sum of its proper divisors (1).

21991511185439 is an equidigital number, since it uses as much as digits as its factorization.

21991511185439 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 3499200, while the sum is 59.

The spelling of 21991511185439 in words is "twenty-one trillion, nine hundred ninety-one billion, five hundred eleven million, one hundred eighty-five thousand, four hundred thirty-nine".