21011221220 has 96 divisors (see below), whose sum is σ = 49326520320. Its totient is φ = 7452397440.

The previous prime is 21011221181. The next prime is 21011221223. The reversal of 21011221220 is 2212211012.

It is a junction number, because it is equal to n+sod(n) for n = 21011221195 and 21011221204.

It is not an unprimeable number, because it can be changed into a prime (21011221223) by changing a digit.

It is a polite number, since it can be written in 31 ways as a sum of consecutive naturals, for example, 3171071 + ... + 3177689.

It is an arithmetic number, because the mean of its divisors is an integer number (513817920).

Almost surely, 2^21011221220 is an apocalyptic number.

21011221220 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21011221220, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (24663260160).

21011221220 is an abundant number, since it is smaller than the sum of its proper divisors (28315299100).

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

21011221220 is a wasteful number, since it uses less digits than its factorization.

21011221220 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 6993 (or 6991 counting only the distinct ones).

The product of its (nonzero) digits is 32, while the sum is 14.

Adding to 21011221220 its reverse (2212211012), we get a palindrome (23223432232).

The spelling of 21011221220 in words is "twenty-one billion, eleven million, two hundred twenty-one thousand, two hundred twenty".