21040 has 20 divisors (see below), whose sum is σ = 49104. Its totient is φ = 8384.

The previous prime is 21031. The next prime is 21059. The reversal of 21040 is 4012.

It is a tau number, because it is divible by the number of its divisors (20).

It is a nialpdrome in base 13.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (5) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 52 + ... + 211.

2²¹⁰⁴⁰ is an apocalyptic number.

21040 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21040 is an abundant number, since it is smaller than the sum of its proper divisors (28064).

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

It is a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (24552).

21040 is a wasteful number, since it uses less digits than its factorization.

21040 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 276 (or 270 counting only the distinct ones).

The product of its (nonzero) digits is 8, while the sum is 7.

The square root of 21040 is about 145.0517149157. The cubic root of 21040 is about 27.6067476326.

Adding to 21040 its reverse (4012), we get a palindrome (25052).

It can be divided in two parts, 2 and 1040, that multiplied together give a triangular number (2080 = T₆₄).

The spelling of 21040 in words is "twenty-one thousand, forty", and thus it is an iban number.