21005312 has 44 divisors (see below), whose sum is σ = 42716796. Its totient is φ = 10321920.

The previous prime is 21005311. The next prime is 21005329. The reversal of 21005312 is 21350012.

It is a happy number.

It can be written as a sum of positive squares in 2 ways, for example, as 13075456 + 7929856 = 3616^2 + 2816^2 .

It is not an unprimeable number, because it can be changed into a prime (21005311) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 74612 + ... + 74892.

Almost surely, 2^21005312 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 21005312, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (21358398).

21005312 is an abundant number, since it is smaller than the sum of its proper divisors (21711484).

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

21005312 is an equidigital number, since it uses as much as digits as its factorization.

21005312 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 374 (or 356 counting only the distinct ones).

The product of its (nonzero) digits is 60, while the sum is 14.

The square root of 21005312 is about 4583.1552450250. The cubic root of 21005312 is about 275.9156782249.

Adding to 21005312 its reverse (21350012), we get a palindrome (42355324).

The spelling of 21005312 in words is "twenty-one million, five thousand, three hundred twelve".