21000209847791 has 2 divisors, whose sum is σ = 21000209847792. Its totient is φ = 21000209847790.

The previous prime is 21000209847733. The next prime is 21000209847857. The reversal of 21000209847791 is 19774890200012.

It is a weak prime.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21000209847791 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21000209849791) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10500104923895 + 10500104923896.

It is an arithmetic number, because the mean of its divisors is an integer number (10500104923896).

Almost surely, 2^{21000209847791} is an apocalyptic number.

21000209847791 is a deficient number, since it is larger than the sum of its proper divisors (1).

21000209847791 is an equidigital number, since it uses as much as digits as its factorization.

21000209847791 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 508032, while the sum is 50.

The spelling of 21000209847791 in words is "twenty-one trillion, two hundred nine million, eight hundred forty-seven thousand, seven hundred ninety-one".