21217907885 has 4 divisors (see below), whose sum is σ = 25461489468. Its totient is φ = 16974326304.

The previous prime is 21217907881. The next prime is 21217907891. The reversal of 21217907885 is 58870971212.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 7370737609 + 13847170276 = 85853^2 + 117674^2 .

It is a cyclic number.

It is not a de Polignac number, because 21217907885 - 2² = 21217907881 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21217907881) 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, 2121790784 + ... + 2121790793.

It is an arithmetic number, because the mean of its divisors is an integer number (6365372367).

Almost surely, 2^21217907885 is an apocalyptic number.

It is an amenable number.

21217907885 is a deficient number, since it is larger than the sum of its proper divisors (4243581583).

21217907885 is an equidigital number, since it uses as much as digits as its factorization.

21217907885 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 4243581582.

The product of its (nonzero) digits is 564480, while the sum is 50.

The spelling of 21217907885 in words is "twenty-one billion, two hundred seventeen million, nine hundred seven thousand, eight hundred eighty-five".