21125553209 has 2 divisors, whose sum is σ = 21125553210. Its totient is φ = 21125553208.

The previous prime is 21125553203. The next prime is 21125553259. The reversal of 21125553209 is 90235552112.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 20720738809 + 404814400 = 143947^2 + 20120^2 .

It is a cyclic number.

It is not a de Polignac number, because 21125553209 - 2¹² = 21125549113 is a prime.

It is not a weakly prime, because it can be changed into another prime (21125553203) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (19) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10562776604 + 10562776605.

It is an arithmetic number, because the mean of its divisors is an integer number (10562776605).

Almost surely, 2^21125553209 is an apocalyptic number.

It is an amenable number.

21125553209 is a deficient number, since it is larger than the sum of its proper divisors (1).

21125553209 is an equidigital number, since it uses as much as digits as its factorization.

21125553209 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 27000, while the sum is 35.

The spelling of 21125553209 in words is "twenty-one billion, one hundred twenty-five million, five hundred fifty-three thousand, two hundred nine".