21878107709 has 4 divisors (see below), whose sum is σ = 21878454780. Its totient is φ = 21877760640.

The previous prime is 21878107661. The next prime is 21878107747. The reversal of 21878107709 is 90770187812.

It is a happy number.

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 701455225 + 21176652484 = 26485^2 + 145522^2 .

It is a cyclic number.

It is not a de Polignac number, because 21878107709 - 2²⁰ = 21877059133 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 (21878107759) 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, 49364 + ... + 214925.

It is an arithmetic number, because the mean of its divisors is an integer number (5469613695).

Almost surely, 2^21878107709 is an apocalyptic number.

It is an amenable number.

21878107709 is a deficient number, since it is larger than the sum of its proper divisors (347071).

21878107709 is an equidigital number, since it uses as much as digits as its factorization.

21878107709 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 347070.

The product of its (nonzero) digits is 395136, while the sum is 50.

The spelling of 21878107709 in words is "twenty-one billion, eight hundred seventy-eight million, one hundred seven thousand, seven hundred nine".