21218408 has 8 divisors (see below), whose sum is σ = 39784530. Its totient is φ = 10609200.

The previous prime is 21218387. The next prime is 21218413. The reversal of 21218408 is 80481212.

It can be written as a sum of positive squares in only one way, i.e., 18852964 + 2365444 = 4342^2 + 1538^2 .

It is a tau number, because it is divible by the number of its divisors (8).

It is an unprimeable number.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 1326143 + ... + 1326158.

Almost surely, 2^21218408 is an apocalyptic number.

It is an amenable number.

21218408 is a deficient number, since it is larger than the sum of its proper divisors (18566122).

21218408 is a wasteful number, since it uses less digits than its factorization.

21218408 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2652307 (or 2652303 counting only the distinct ones).

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

The square root of 21218408 is about 4606.3443206083. The cubic root of 21218408 is about 276.8455828904.

The spelling of 21218408 in words is "twenty-one million, two hundred eighteen thousand, four hundred eight".