21331220 has 12 divisors (see below), whose sum is σ = 44795604. Its totient is φ = 8532480.

The previous prime is 21331217. The next prime is 21331267. The reversal of 21331220 is 2213312.

It is a happy number.

It can be written as a sum of positive squares in 2 ways, for example, as 16032016 + 5299204 = 4004^2 + 2302^2 .

It is a junction number, because it is equal to n+sod(n) for n = 21331195 and 21331204.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 533261 + ... + 533300.

It is an arithmetic number, because the mean of its divisors is an integer number (3732967).

Almost surely, 2^21331220 is an apocalyptic number.

21331220 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21331220 is an abundant number, since it is smaller than the sum of its proper divisors (23464384).

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

21331220 is a wasteful number, since it uses less digits than its factorization.

21331220 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1066570 (or 1066568 counting only the distinct ones).

The product of its (nonzero) digits is 72, while the sum is 14.

The square root of 21331220 is about 4618.5733728068. The cubic root of 21331220 is about 277.3353512910.

Adding to 21331220 its reverse (2213312), we get a palindrome (23544532).

The spelling of 21331220 in words is "twenty-one million, three hundred thirty-one thousand, two hundred twenty".