21405588170261 has 4 divisors (see below), whose sum is σ = 22143711900300. Its totient is φ = 20667464440224.

The previous prime is 21405588170207. The next prime is 21405588170273. The reversal of 21405588170261 is 16207188550412.

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 16291798416100 + 5113789754161 = 4036310^2 + 2261369^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21405588170261 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 (21405588175261) 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, 369061864976 + ... + 369061865033.

It is an arithmetic number, because the mean of its divisors is an integer number (5535927975075).

Almost surely, 2^{21405588170261} is an apocalyptic number.

It is an amenable number.

21405588170261 is a deficient number, since it is larger than the sum of its proper divisors (738123730039).

21405588170261 is an equidigital number, since it uses as much as digits as its factorization.

21405588170261 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 738123730038.

The product of its (nonzero) digits is 1075200, while the sum is 50.

The spelling of 21405588170261 in words is "twenty-one trillion, four hundred five billion, five hundred eighty-eight million, one hundred seventy thousand, two hundred sixty-one".