21218851 has 8 divisors (see below), whose sum is σ = 21467600. Its totient is φ = 20971872.

The previous prime is 21218831. The next prime is 21218861. The reversal of 21218851 is 15881212.

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

It is a cyclic number.

It is not a de Polignac number, because 21218851 - 2¹⁷ = 21087779 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21218831) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 56701 + ... + 57073.

It is an arithmetic number, because the mean of its divisors is an integer number (2683450).

Almost surely, 2^21218851 is an apocalyptic number.

21218851 is a deficient number, since it is larger than the sum of its proper divisors (248749).

21218851 is a wasteful number, since it uses less digits than its factorization.

21218851 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 885.

The product of its digits is 1280, while the sum is 28.

The square root of 21218851 is about 4606.3924062112. The cubic root of 21218851 is about 276.8475095467.

The spelling of 21218851 in words is "twenty-one million, two hundred eighteen thousand, eight hundred fifty-one".