21561212 has 12 divisors (see below), whose sum is σ = 39372816. Its totient is φ = 10311840.

The previous prime is 21561193. The next prime is 21561223. The reversal of 21561212 is 21216512.

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, 117089 + ... + 117272.

It is an arithmetic number, because the mean of its divisors is an integer number (3281068).

Almost surely, 2^21561212 is an apocalyptic number.

It is an amenable number.

21561212 is a deficient number, since it is larger than the sum of its proper divisors (17811604).

21561212 is a wasteful number, since it uses less digits than its factorization.

21561212 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 234388 (or 234386 counting only the distinct ones).

The product of its digits is 240, while the sum is 20.

The square root of 21561212 is about 4643.4052160026. The cubic root of 21561212 is about 278.3285283293.

Adding to 21561212 its reverse (21216512), we get a palindrome (42777724).

The spelling of 21561212 in words is "twenty-one million, five hundred sixty-one thousand, two hundred twelve".