21121220 has 12 divisors (see below), whose sum is σ = 44354604. Its totient is φ = 8448480.

The previous prime is 21121211. The next prime is 21121223. The reversal of 21121220 is 2212112.

It is a happy number.

It can be written as a sum of positive squares in 2 ways, for example, as 7043716 + 14077504 = 2654^2 + 3752^2 .

It is a super-2 number, since 2×21121220² = 892211868576800, which contains 22 as substring.

It is not an unprimeable number, because it can be changed into a prime (21121223) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 528011 + ... + 528050.

It is an arithmetic number, because the mean of its divisors is an integer number (3696217).

Almost surely, 2^21121220 is an apocalyptic number.

21121220 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21121220 is an abundant number, since it is smaller than the sum of its proper divisors (23233384).

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

21121220 is a wasteful number, since it uses less digits than its factorization.

21121220 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1056070 (or 1056068 counting only the distinct ones).

The product of its (nonzero) digits is 16, while the sum is 11.

The square root of 21121220 is about 4595.7828495263. The cubic root of 21121220 is about 276.4222515199.

Adding to 21121220 its reverse (2212112), we get a palindrome (23333332).

The spelling of 21121220 in words is "twenty-one million, one hundred twenty-one thousand, two hundred twenty".