21165615209 has 2 divisors, whose sum is σ = 21165615210. Its totient is φ = 21165615208.

The previous prime is 21165615199. The next prime is 21165615217. The reversal of 21165615209 is 90251656112.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 20493354025 + 672261184 = 143155^2 + 25928^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21165615209 is a prime.

It is a super-3 number, since 3×21165615209³ (a number of 32 digits) contains 333 as substring. Note that it is a super-d number also for d = 2.

It is not a weakly prime, because it can be changed into another prime (21165618209) 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, 10582807604 + 10582807605.

It is an arithmetic number, because the mean of its divisors is an integer number (10582807605).

Almost surely, 2^21165615209 is an apocalyptic number.

It is an amenable number.

21165615209 is a deficient number, since it is larger than the sum of its proper divisors (1).

21165615209 is an equidigital number, since it uses as much as digits as its factorization.

21165615209 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 32400, while the sum is 38.

The spelling of 21165615209 in words is "twenty-one billion, one hundred sixty-five million, six hundred fifteen thousand, two hundred nine".