21535540 has 48 divisors (see below), whose sum is σ = 49201488. Its totient is φ = 7870464.

The previous prime is 21535529. The next prime is 21535589. The reversal of 21535540 is 4553512.

It can be written as a sum of positive squares in 8 ways, for example, as 1572516 + 19963024 = 1254^2 + 4468^2 .

It is a congruent number.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 29014 + ... + 29746.

It is an arithmetic number, because the mean of its divisors is an integer number (1025031).

Almost surely, 2^21535540 is an apocalyptic number.

21535540 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 21535540, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (24600744).

21535540 is an abundant number, since it is smaller than the sum of its proper divisors (27665948).

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

21535540 is a wasteful number, since it uses less digits than its factorization.

21535540 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 868 (or 866 counting only the distinct ones).

The product of its (nonzero) digits is 3000, while the sum is 25.

The square root of 21535540 is about 4640.6400420632. The cubic root of 21535540 is about 278.2180198894.

The spelling of 21535540 in words is "twenty-one million, five hundred thirty-five thousand, five hundred forty".