21521940 has 48 divisors (see below), whose sum is σ = 65741760. Its totient is φ = 5217280.

The previous prime is 21521939. The next prime is 21521947. The reversal of 21521940 is 4912512.

It is a self number, because there is not a number n which added to its sum of digits gives 21521940.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21521947) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 15645 + ... + 16964.

It is an arithmetic number, because the mean of its divisors is an integer number (1369620).

Almost surely, 2^21521940 is an apocalyptic number.

21521940 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21521940 is an abundant number, since it is smaller than the sum of its proper divisors (44219820).

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

21521940 is a wasteful number, since it uses less digits than its factorization.

21521940 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 32632 (or 32630 counting only the distinct ones).

The product of its (nonzero) digits is 720, while the sum is 24.

The square root of 21521940 is about 4639.1744955326. The cubic root of 21521940 is about 278.1594413435.

It can be divided in two parts, 215 and 21940, that added together give a triangular number (22155 = T₂₁₀).

The spelling of 21521940 in words is "twenty-one million, five hundred twenty-one thousand, nine hundred forty".