21216464 has 40 divisors (see below), whose sum is σ = 43762080. Its totient is φ = 9936000.

The previous prime is 21216457. The next prime is 21216467. The reversal of 21216464 is 46461212.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21216467) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 30359 + ... + 31049.

It is an arithmetic number, because the mean of its divisors is an integer number (1094052).

Almost surely, 2^21216464 is an apocalyptic number.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21216464, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (21881040).

21216464 is an abundant number, since it is smaller than the sum of its proper divisors (22545616).

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

21216464 is a wasteful number, since it uses less digits than its factorization.

21216464 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 819 (or 813 counting only the distinct ones).

The product of its digits is 2304, while the sum is 26.

The square root of 21216464 is about 4606.1333024566. The cubic root of 21216464 is about 276.8371279009.

Adding to 21216464 its reverse (46461212), we get a palindrome (67677676).

The spelling of 21216464 in words is "twenty-one million, two hundred sixteen thousand, four hundred sixty-four".