21111220 has 24 divisors (see below), whose sum is σ = 47744424. Its totient is φ = 7794816.

The previous prime is 21111199. The next prime is 21111239. The reversal of 21111220 is 2211112.

It can be written as a sum of positive squares in 4 ways, for example, as 698896 + 20412324 = 836^2 + 4518^2 .

It is a Harshad number since it is a multiple of its sum of digits (10).

It is a junction number, because it is equal to n+sod(n) for n = 21111197 and 21111206.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 40339 + ... + 40858.

It is an arithmetic number, because the mean of its divisors is an integer number (1989351).

Almost surely, 2^21111220 is an apocalyptic number.

21111220 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21111220 is an abundant number, since it is smaller than the sum of its proper divisors (26633204).

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

21111220 is a wasteful number, since it uses less digits than its factorization.

21111220 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 81219 (or 81217 counting only the distinct ones).

The product of its (nonzero) digits is 8, while the sum is 10.

The square root of 21111220 is about 4594.6947667935. The cubic root of 21111220 is about 276.3786199040.

Adding to 21111220 its reverse (2211112), we get a palindrome (23322332).

The spelling of 21111220 in words is "twenty-one million, one hundred eleven thousand, two hundred twenty".