21871581123521 has 4 divisors (see below), whose sum is σ = 21871606463700. Its totient is φ = 21871555783344.

The previous prime is 21871581123473. The next prime is 21871581123529. The reversal of 21871581123521 is 12532118517812.

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 4099454633521 + 17772126490000 = 2024711^2 + 4215700^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21871581123521 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21871581123529) 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, 11328026 + ... + 13117443.

It is an arithmetic number, because the mean of its divisors is an integer number (5467901615925).

Almost surely, 2^{21871581123521} is an apocalyptic number.

It is an amenable number.

21871581123521 is a deficient number, since it is larger than the sum of its proper divisors (25340179).

21871581123521 is an equidigital number, since it uses as much as digits as its factorization.

21871581123521 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 25340178.

The product of its digits is 268800, while the sum is 47.

The spelling of 21871581123521 in words is "twenty-one trillion, eight hundred seventy-one billion, five hundred eighty-one million, one hundred twenty-three thousand, five hundred twenty-one".