21801858561 has 48 divisors (see below), whose sum is σ = 37618358400. Its totient is φ = 12442955616.

The previous prime is 21801858511. The next prime is 21801858563. The reversal of 21801858561 is 16585810812.

21801858561 is a `hidden beast` number, since 2 + 1 + 8 + 0 + 1 + 8 + 585 + 61 = 666.

It is not a de Polignac number, because 21801858561 - 2²³ = 21793469953 is a prime.

It is not an unprimeable number, because it can be changed into a prime (21801858563) by changing a digit.

It is a polite number, since it can be written in 47 ways as a sum of consecutive naturals, for example, 1118860 + ... + 1138178.

It is an arithmetic number, because the mean of its divisors is an integer number (783715800).

Almost surely, 2^21801858561 is an apocalyptic number.

21801858561 is a gapful number since it is divisible by the number (21) formed by its first and last digit.

It is an amenable number.

21801858561 is a deficient number, since it is larger than the sum of its proper divisors (15816499839).

21801858561 is a wasteful number, since it uses less digits than its factorization.

21801858561 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 20195 (or 20182 counting only the distinct ones).

The product of its (nonzero) digits is 153600, while the sum is 45.

The spelling of 21801858561 in words is "twenty-one billion, eight hundred one million, eight hundred fifty-eight thousand, five hundred sixty-one".