21218456 has 16 divisors (see below), whose sum is σ = 45468240. Its totient is φ = 9093600.

The previous prime is 21218441. The next prime is 21218467. The reversal of 21218456 is 65481212.

It is a congruent number.

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, 189395 + ... + 189506.

It is an arithmetic number, because the mean of its divisors is an integer number (2841765).

Almost surely, 2^21218456 is an apocalyptic number.

It is an amenable number.

21218456 is an abundant number, since it is smaller than the sum of its proper divisors (24249784).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

21218456 is a wasteful number, since it uses less digits than its factorization.

21218456 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 378914 (or 378910 counting only the distinct ones).

The product of its digits is 3840, while the sum is 29.

The square root of 21218456 is about 4606.3495308107. The cubic root of 21218456 is about 276.8457916490.

Adding to 21218456 its reverse (65481212), we get a palindrome (86699668).

The spelling of 21218456 in words is "twenty-one million, two hundred eighteen thousand, four hundred fifty-six".