21009808249 has 2 divisors, whose sum is σ = 21009808250. Its totient is φ = 21009808248.

The previous prime is 21009808231. The next prime is 21009808273. The reversal of 21009808249 is 94280890012.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 19413406224 + 1596402025 = 139332^2 + 39955^2 .

It is a cyclic number.

It is not a de Polignac number, because 21009808249 - 2⁹ = 21009807737 is a prime.

It is not a weakly prime, because it can be changed into another prime (21009808279) 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, 10504904124 + 10504904125.

It is an arithmetic number, because the mean of its divisors is an integer number (10504904125).

Almost surely, 2^21009808249 is an apocalyptic number.

It is an amenable number.

21009808249 is a deficient number, since it is larger than the sum of its proper divisors (1).

21009808249 is an equidigital number, since it uses as much as digits as its factorization.

21009808249 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 82944, while the sum is 43.

The spelling of 21009808249 in words is "twenty-one billion, nine million, eight hundred eight thousand, two hundred forty-nine".