21218810 has 8 divisors (see below), whose sum is σ = 38193876. Its totient is φ = 8487520.

The previous prime is 21218809. The next prime is 21218831. The reversal of 21218810 is 1881212.

It is a happy number.

It can be written as a sum of positive squares in 2 ways, for example, as 20421361 + 797449 = 4519^2 + 893^2 .

It is a sphenic number, since it is the product of 3 distinct primes.

It is a super-2 number, since 2×21218810² = 900475795632200, which contains 22 as substring.

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, 1060931 + ... + 1060950.

Almost surely, 2^21218810 is an apocalyptic number.

21218810 is a deficient number, since it is larger than the sum of its proper divisors (16975066).

21218810 is a wasteful number, since it uses less digits than its factorization.

21218810 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2121888.

The product of its (nonzero) digits is 256, while the sum is 23.

The square root of 21218810 is about 4606.3879558717. The cubic root of 21218810 is about 276.8473312342.

The spelling of 21218810 in words is "twenty-one million, two hundred eighteen thousand, eight hundred ten".