21221210 has 16 divisors (see below), whose sum is σ = 38550600. Its totient is φ = 8410176.

The previous prime is 21221171. The next prime is 21221237. The reversal of 21221210 is 1212212.

21221210 = T₂₉₁₁ + T₂₉₁₂ + ... + T₂₉₁₅.

It is a happy number.

It can be written as a sum of positive squares in 4 ways, for example, as 17530969 + 3690241 = 4187^2 + 1921^2 .

It is a junction number, because it is equal to n+sod(n) for n = 21221191 and 21221200.

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, 8645 + ... + 10824.

Almost surely, 2^21221210 is an apocalyptic number.

21221210 is a deficient number, since it is larger than the sum of its proper divisors (17329390).

21221210 is a wasteful number, since it uses less digits than its factorization.

21221210 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 19585.

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

The square root of 21221210 is about 4606.6484563075. The cubic root of 21221210 is about 276.8577686487.

Adding to 21221210 its reverse (1212212), we get a palindrome (22433422).

The spelling of 21221210 in words is "twenty-one million, two hundred twenty-one thousand, two hundred ten".