21221515818 has 48 divisors (see below), whose sum is σ = 46466429256. Its totient is φ = 6999091200.

The previous prime is 21221515793. The next prime is 21221515829. The reversal of 21221515818 is 81851512212.

21221515818 is a `hidden beast` number, since 2 + 1 + 2 + 21 + 51 + 581 + 8 = 666.

It can be written as a sum of positive squares in 4 ways, for example, as 19419258609 + 1802257209 = 139353^2 + 42453^2 .

It is a super-2 number, since 2×21221515818² (a number of 21 digits) contains 22 as substring.

It is a Curzon number.

It is an unprimeable number.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 3620346 + ... + 3626202.

Almost surely, 2^21221515818 is an apocalyptic number.

21221515818 is an abundant number, since it is smaller than the sum of its proper divisors (25244913438).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

21221515818 is a wasteful number, since it uses less digits than its factorization.

21221515818 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 7959 (or 7956 counting only the distinct ones).

The product of its digits is 12800, while the sum is 36.

The spelling of 21221515818 in words is "twenty-one billion, two hundred twenty-one million, five hundred fifteen thousand, eight hundred eighteen".