21298378891 has 4 divisors (see below), whose sum is σ = 21793690072. Its totient is φ = 20803067712.

The previous prime is 21298378873. The next prime is 21298378897. The reversal of 21298378891 is 19887389212.

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 21298378891 - 2¹³ = 21298370699 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21298378897) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 247655526 + ... + 247655611.

It is an arithmetic number, because the mean of its divisors is an integer number (5448422518).

Almost surely, 2^21298378891 is an apocalyptic number.

21298378891 is a deficient number, since it is larger than the sum of its proper divisors (495311181).

21298378891 is an equidigital number, since it uses as much as digits as its factorization.

21298378891 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 495311180.

The product of its digits is 3483648, while the sum is 58.

The spelling of 21298378891 in words is "twenty-one billion, two hundred ninety-eight million, three hundred seventy-eight thousand, eight hundred ninety-one".