21405340 has 48 divisors (see below), whose sum is σ = 49442400. Its totient is φ = 7719680.

The previous prime is 21405337. The next prime is 21405359. The reversal of 21405340 is 4350412.

It is a congruent number.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 32454 + ... + 33106.

It is an arithmetic number, because the mean of its divisors is an integer number (1030050).

Almost surely, 2^21405340 is an apocalyptic number.

21405340 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21405340, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (24721200).

21405340 is an abundant number, since it is smaller than the sum of its proper divisors (28037060).

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

21405340 is a wasteful number, since it uses less digits than its factorization.

21405340 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 822 (or 820 counting only the distinct ones).

The product of its (nonzero) digits is 480, while the sum is 19.

The square root of 21405340 is about 4626.5905373180. The cubic root of 21405340 is about 277.6562007815.

Adding to 21405340 its reverse (4350412), we get a palindrome (25755752).

The spelling of 21405340 in words is "twenty-one million, four hundred five thousand, three hundred forty".