21621312 has 42 divisors (see below), whose sum is σ = 61975238. Its totient is φ = 7206912.

The previous prime is 21621293. The next prime is 21621329. The reversal of 21621312 is 21312612.

It can be written as a sum of positive squares in only one way, i.e., 17842176 + 3779136 = 4224^2 + 1944^2 .

It is a super-2 number, since 2×21621312² = 934962265202688, which contains 22 as substring.

It is a Harshad number since it is a multiple of its sum of digits (18).

It is a nude number because it is divisible by every one of its digits and also a Zuckerman number because it is divisible by the product of its digits.

It is an unprimeable number.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 18193 + ... + 19344.

Almost surely, 2^21621312 is an apocalyptic number.

It is an amenable number.

21621312 is an abundant number, since it is smaller than the sum of its proper divisors (40353926).

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

21621312 is a wasteful number, since it uses less digits than its factorization.

21621312 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 37555 (or 37542 counting only the distinct ones).

The product of its digits is 144, while the sum is 18.

The square root of 21621312 is about 4649.8722563098. The cubic root of 21621312 is about 278.5868939287.

Adding to 21621312 its reverse (21312612), we get a palindrome (42933924).

It can be divided in two parts, 216213 and 12, that added together give a square (216225 = 465²).

The spelling of 21621312 in words is "twenty-one million, six hundred twenty-one thousand, three hundred twelve".