21211211220 has 72 divisors (see below), whose sum is σ = 61369211232. Its totient is φ = 5473846080.

The previous prime is 21211211213. The next prime is 21211211227. The reversal of 21211211220 is 2211211212.

It is an interprime number because it is at equal distance from previous prime (21211211213) and next prime (21211211227).

It is a Harshad number since it is a multiple of its sum of digits (15).

It is a self number, because there is not a number n which added to its sum of digits gives 21211211220.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21211211227) by changing a digit.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 126274 + ... + 241593.

It is an arithmetic number, because the mean of its divisors is an integer number (852350156).

Almost surely, 2^21211211220 is an apocalyptic number.

21211211220 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21211211220 is an abundant number, since it is smaller than the sum of its proper divisors (40158000012).

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

21211211220 is a wasteful number, since it uses less digits than its factorization.

21211211220 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 367941 (or 367908 counting only the distinct ones).

The product of its (nonzero) digits is 32, while the sum is 15.

Adding to 21211211220 its reverse (2211211212), we get a palindrome (23422422432).

The spelling of 21211211220 in words is "twenty-one billion, two hundred eleven million, two hundred eleven thousand, two hundred twenty".