21581781715841 has 4 divisors (see below), whose sum is σ = 21581949713712. Its totient is φ = 21581613717972.

The previous prime is 21581781715829. The next prime is 21581781715843. The reversal of 21581781715841 is 14851718718512.

It is a happy number.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is not a de Polignac number, because 21581781715841 - 2³⁰ = 21580707974017 is a prime.

It is a Duffinian number.

It is a Curzon number.

It is not an unprimeable number, because it can be changed into a prime (21581781715843) 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, 83806091 + ... + 84063216.

It is an arithmetic number, because the mean of its divisors is an integer number (5395487428428).

Almost surely, 2^{21581781715841} is an apocalyptic number.

It is an amenable number.

21581781715841 is a deficient number, since it is larger than the sum of its proper divisors (167997871).

21581781715841 is a wasteful number, since it uses less digits than its factorization.

21581781715841 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 167997870.

The product of its digits is 5017600, while the sum is 59.

The spelling of 21581781715841 in words is "twenty-one trillion, five hundred eighty-one billion, seven hundred eighty-one million, seven hundred fifteen thousand, eight hundred forty-one".