21381540 has 48 divisors (see below), whose sum is σ = 60079488. Its totient is φ = 5681664.

The previous prime is 21381539. The next prime is 21381553. The reversal of 21381540 is 4518312.

It is a self number, because there is not a number n which added to its sum of digits gives 21381540.

It is an unprimeable number.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 25569 + ... + 26391.

It is an arithmetic number, because the mean of its divisors is an integer number (1251656).

Almost surely, 2^21381540 is an apocalyptic number.

21381540 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21381540 is an abundant number, since it is smaller than the sum of its proper divisors (38697948).

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

21381540 is a wasteful number, since it uses less digits than its factorization.

21381540 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1268 (or 1266 counting only the distinct ones).

The product of its (nonzero) digits is 960, while the sum is 24.

The square root of 21381540 is about 4624.0177335300. The cubic root of 21381540 is about 277.5532565589.

Adding to 21381540 its reverse (4518312), we get a palindrome (25899852).

The spelling of 21381540 in words is "twenty-one million, three hundred eighty-one thousand, five hundred forty".