21385540 has 36 divisors (see below), whose sum is σ = 49369068. Its totient is φ = 7775680.

The previous prime is 21385513. The next prime is 21385549. The reversal of 21385540 is 4558312.

It can be written as a sum of positive squares in 2 ways, for example, as 16924996 + 4460544 = 4114^2 + 2112^2 .

It is a junction number, because it is equal to n+sod(n) for n = 21385499 and 21385508.

It is not an unprimeable number, because it can be changed into a prime (21385549) 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, 1999 + ... + 6838.

It is an arithmetic number, because the mean of its divisors is an integer number (1371363).

Almost surely, 2^21385540 is an apocalyptic number.

21385540 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21385540 is an abundant number, since it is smaller than the sum of its proper divisors (27983528).

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

21385540 is a wasteful number, since it uses less digits than its factorization.

21385540 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 8868 (or 8855 counting only the distinct ones).

The product of its (nonzero) digits is 4800, while the sum is 28.

The square root of 21385540 is about 4624.4502375958. The cubic root of 21385540 is about 277.5705634476.

The spelling of 21385540 in words is "twenty-one million, three hundred eighty-five thousand, five hundred forty".