21009818 has 8 divisors (see below), whose sum is σ = 31827060. Its totient is φ = 10400800.

The previous prime is 21009761. The next prime is 21009827. The reversal of 21009818 is 81890012.

It can be written as a sum of positive squares in 2 ways, for example, as 21003889 + 5929 = 4583^2 + 77^2 .

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

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, 51803 + ... + 52206.

Almost surely, 2^21009818 is an apocalyptic number.

21009818 is a deficient number, since it is larger than the sum of its proper divisors (10817242).

21009818 is a wasteful number, since it uses less digits than its factorization.

21009818 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 104112.

The product of its (nonzero) digits is 1152, while the sum is 29.

The square root of 21009818 is about 4583.6468014017. The cubic root of 21009818 is about 275.9354063641.

The spelling of 21009818 in words is "twenty-one million, nine thousand, eight hundred eighteen".