21405312 has 96 divisors (see below), whose sum is σ = 65278980. Its totient is φ = 6709248.

The previous prime is 21405299. The next prime is 21405313. The reversal of 21405312 is 21350412.

It can be written as a sum of positive squares in 2 ways, for example, as 16842816 + 4562496 = 4104^2 + 2136^2 .

It is a tau number, because it is divible by the number of its divisors (96).

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

It is not an unprimeable number, because it can be changed into a prime (21405313) by changing a digit.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 19038 + ... + 20130.

Almost surely, 2^21405312 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 21405312, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (32639490).

21405312 is an abundant number, since it is smaller than the sum of its proper divisors (43873668).

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

21405312 is a wasteful number, since it uses less digits than its factorization.

21405312 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1130 (or 1115 counting only the distinct ones).

The product of its (nonzero) digits is 240, while the sum is 18.

The square root of 21405312 is about 4626.5875113306. The cubic root of 21405312 is about 277.6560797155.

Adding to 21405312 its reverse (21350412), we get a palindrome (42755724).

The spelling of 21405312 in words is "twenty-one million, four hundred five thousand, three hundred twelve".