21815807181 has 16 divisors (see below), whose sum is σ = 33616656000. Its totient is φ = 12326105088.

The previous prime is 21815807099. The next prime is 21815807203. The reversal of 21815807181 is 18170851812.

It is not a de Polignac number, because 21815807181 - 2²¹ = 21813710029 is a prime.

It is a super-2 number, since 2×21815807181² (a number of 21 digits) contains 22 as substring.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21815807081) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 5834356 + ... + 5838093.

It is an arithmetic number, because the mean of its divisors is an integer number (2101041000).

Almost surely, 2^21815807181 is an apocalyptic number.

21815807181 is a gapful number since it is divisible by the number (21) formed by its first and last digit.

It is an amenable number.

21815807181 is a deficient number, since it is larger than the sum of its proper divisors (11800848819).

21815807181 is a wasteful number, since it uses less digits than its factorization.

21815807181 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 11672548.

The product of its (nonzero) digits is 35840, while the sum is 42.

The spelling of 21815807181 in words is "twenty-one billion, eight hundred fifteen million, eight hundred seven thousand, one hundred eighty-one".