21506205521741 has 4 divisors (see below), whose sum is σ = 21509475439452. Its totient is φ = 21502935604032.

The previous prime is 21506205521681. The next prime is 21506205521771. The reversal of 21506205521741 is 14712550260512.

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 9911131758025 + 11595073763716 = 3148195^2 + 3405154^2 .

It is a cyclic number.

It is not a de Polignac number, because 21506205521741 - 2³⁴ = 21489025652557 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 (21506205521771) 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, 1634948990 + ... + 1634962143.

It is an arithmetic number, because the mean of its divisors is an integer number (5377368859863).

Almost surely, 2^{21506205521741} is an apocalyptic number.

It is an amenable number.

21506205521741 is a deficient number, since it is larger than the sum of its proper divisors (3269917711).

21506205521741 is an equidigital number, since it uses as much as digits as its factorization.

21506205521741 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 3269917710.

The product of its (nonzero) digits is 168000, while the sum is 41.

The spelling of 21506205521741 in words is "twenty-one trillion, five hundred six billion, two hundred five million, five hundred twenty-one thousand, seven hundred forty-one".