21000209847857 has 2 divisors, whose sum is σ = 21000209847858. Its totient is φ = 21000209847856.

The previous prime is 21000209847791. The next prime is 21000209847887. The reversal of 21000209847857 is 75874890200012.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 20984974636096 + 15235211761 = 4580936^2 + 123431^2 .

It is a cyclic number.

It is not a de Polignac number, because 21000209847857 - 2⁸ = 21000209847601 is a prime.

It is a junction number, because it is equal to n+sod(n) for n = 21000209847799 and 21000209847808.

It is not a weakly prime, because it can be changed into another prime (21000209847887) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10500104923928 + 10500104923929.

It is an arithmetic number, because the mean of its divisors is an integer number (10500104923929).

Almost surely, 2^{21000209847857} is an apocalyptic number.

It is an amenable number.

21000209847857 is a deficient number, since it is larger than the sum of its proper divisors (1).

21000209847857 is an equidigital number, since it uses as much as digits as its factorization.

21000209847857 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 2257920, while the sum is 53.

The spelling of 21000209847857 in words is "twenty-one trillion, two hundred nine million, eight hundred forty-seven thousand, eight hundred fifty-seven".