21218228 has 6 divisors (see below), whose sum is σ = 37131906. Its totient is φ = 10609112.

The previous prime is 21218191. The next prime is 21218233. The reversal of 21218228 is 82281212.

It can be written as a sum of positive squares in only one way, i.e., 18992164 + 2226064 = 4358^2 + 1492^2 .

It is a junction number, because it is equal to n+sod(n) for n = 21218197 and 21218206.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 2652275 + ... + 2652282.

It is an arithmetic number, because the mean of its divisors is an integer number (6188651).

Almost surely, 2^21218228 is an apocalyptic number.

It is an amenable number.

21218228 is a deficient number, since it is larger than the sum of its proper divisors (15913678).

21218228 is a wasteful number, since it uses less digits than its factorization.

21218228 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 5304561 (or 5304559 counting only the distinct ones).

The product of its digits is 1024, while the sum is 26.

The square root of 21218228 is about 4606.3247822966. The cubic root of 21218228 is about 276.8448000427.

The spelling of 21218228 in words is "twenty-one million, two hundred eighteen thousand, two hundred twenty-eight".