21406740 has 96 divisors (see below), whose sum is σ = 65608704. Its totient is φ = 5191680.

The previous prime is 21406729. The next prime is 21406747. The reversal of 21406740 is 4760412.

It is a self number, because there is not a number n which added to its sum of digits gives 21406740.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21406747) by changing a digit.

It is a polite number, since it can be written in 31 ways as a sum of consecutive naturals, for example, 31282 + ... + 31958.

It is an arithmetic number, because the mean of its divisors is an integer number (683424).

Almost surely, 2^21406740 is an apocalyptic number.

21406740 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 21406740, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (32804352).

21406740 is an abundant number, since it is smaller than the sum of its proper divisors (44201964).

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

21406740 is a wasteful number, since it uses less digits than its factorization.

21406740 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 737 (or 735 counting only the distinct ones).

The product of its (nonzero) digits is 1344, while the sum is 24.

The square root of 21406740 is about 4626.7418341636. The cubic root of 21406740 is about 277.6622539471.

The spelling of 21406740 in words is "twenty-one million, four hundred six thousand, seven hundred forty".