21020838991 has 2 divisors, whose sum is σ = 21020838992. Its totient is φ = 21020838990.

The previous prime is 21020838977. The next prime is 21020839039. The reversal of 21020838991 is 19983802012.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 21020838991 - 2¹¹ = 21020836943 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21020838911) 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, 10510419495 + 10510419496.

It is an arithmetic number, because the mean of its divisors is an integer number (10510419496).

Almost surely, 2^21020838991 is an apocalyptic number.

21020838991 is a deficient number, since it is larger than the sum of its proper divisors (1).

21020838991 is an equidigital number, since it uses as much as digits as its factorization.

21020838991 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 62208, while the sum is 43.

The spelling of 21020838991 in words is "twenty-one billion, twenty million, eight hundred thirty-eight thousand, nine hundred ninety-one".