215665521861 has 4 divisors (see below), whose sum is σ = 287554029152. Its totient is φ = 143777014572.

The previous prime is 215665521853. The next prime is 215665521871. The reversal of 215665521861 is 168125566512.

215665521861 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is not a de Polignac number, because 215665521861 - 2³ = 215665521853 is a prime.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 215665521861.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (215665521811) 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 in 3 ways as a sum of consecutive naturals, for example, 35944253641 + ... + 35944253646.

It is an arithmetic number, because the mean of its divisors is an integer number (71888507288).

Almost surely, 2^215665521861 is an apocalyptic number.

It is an amenable number.

215665521861 is a deficient number, since it is larger than the sum of its proper divisors (71888507291).

215665521861 is an equidigital number, since it uses as much as digits as its factorization.

215665521861 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 71888507290.

The product of its digits is 864000, while the sum is 48.

The spelling of 215665521861 in words is "two hundred fifteen billion, six hundred sixty-five million, five hundred twenty-one thousand, eight hundred sixty-one".