21208128247 has 4 divisors (see below), whose sum is σ = 21219216480. Its totient is φ = 21197040016.

The previous prime is 21208128233. The next prime is 21208128281. The reversal of 21208128247 is 74282180212.

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

It is a cyclic number.

It is not a de Polignac number, because 21208128247 - 2¹⁹ = 21207603959 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 (21208128217) 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, 5541247 + ... + 5545072.

It is an arithmetic number, because the mean of its divisors is an integer number (5304804120).

Almost surely, 2^21208128247 is an apocalyptic number.

21208128247 is a deficient number, since it is larger than the sum of its proper divisors (11088233).

21208128247 is a wasteful number, since it uses less digits than its factorization.

21208128247 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 11088232.

The product of its (nonzero) digits is 28672, while the sum is 37.

The spelling of 21208128247 in words is "twenty-one billion, two hundred eight million, one hundred twenty-eight thousand, two hundred forty-seven".