21311231220 has 72 divisors (see below), whose sum is σ = 67038308064. Its totient is φ = 5682993696.

The previous prime is 21311231219. The next prime is 21311231237. The reversal of 21311231220 is 2213211312.

21311231220 is a `hidden beast` number, since 21 + 311 + 2 + 312 + 20 = 666.

It is a super-2 number, since 2×21311231220² (a number of 21 digits) contains 22 as substring.

It is a Harshad number since it is a multiple of its sum of digits (18).

It is a junction number, because it is equal to n+sod(n) for n = 21311231193 and 21311231202.

It is a congruent 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, 2187654 + ... + 2197373.

It is an arithmetic number, because the mean of its divisors is an integer number (931087612).

Almost surely, 2^21311231220 is an apocalyptic number.

21311231220 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21311231220 is an abundant number, since it is smaller than the sum of its proper divisors (45727076844).

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

21311231220 is a wasteful number, since it uses less digits than its factorization.

21311231220 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 4385051 (or 4385037 counting only the distinct ones).

The product of its (nonzero) digits is 144, while the sum is 18.

Adding to 21311231220 its reverse (2213211312), we get a palindrome (23524442532).

The spelling of 21311231220 in words is "twenty-one billion, three hundred eleven million, two hundred thirty-one thousand, two hundred twenty".