21381640 has 48 divisors (see below), whose sum is σ = 55968300. Its totient is φ = 7330176.

The previous prime is 21381617. The next prime is 21381653. The reversal of 21381640 is 4618312.

It can be written as a sum of positive squares in 2 ways, for example, as 20448484 + 933156 = 4522^2 + 966^2 .

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (7) of ones.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 3495 + ... + 7414.

Almost surely, 2^21381640 is an apocalyptic number.

21381640 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21381640 is an abundant number, since it is smaller than the sum of its proper divisors (34586660).

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

21381640 is a wasteful number, since it uses less digits than its factorization.

21381640 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 10934 (or 10923 counting only the distinct ones).

The product of its (nonzero) digits is 1152, while the sum is 25.

The square root of 21381640 is about 4624.0285466247. The cubic root of 21381640 is about 277.5536892574.

Adding to 21381640 its reverse (4618312), we get a palindrome (25999952).

The spelling of 21381640 in words is "twenty-one million, three hundred eighty-one thousand, six hundred forty".