21331540 has 12 divisors (see below), whose sum is σ = 44796276. Its totient is φ = 8532608.

The previous prime is 21331537. The next prime is 21331543. The reversal of 21331540 is 4513312.

It is an interprime number because it is at equal distance from previous prime (21331537) and next prime (21331543).

It can be written as a sum of positive squares in 2 ways, for example, as 3370896 + 17960644 = 1836^2 + 4238^2 .

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21331543) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 533269 + ... + 533308.

It is an arithmetic number, because the mean of its divisors is an integer number (3733023).

Almost surely, 2^21331540 is an apocalyptic number.

21331540 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21331540 is an abundant number, since it is smaller than the sum of its proper divisors (23464736).

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

21331540 is a wasteful number, since it uses less digits than its factorization.

21331540 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1066586 (or 1066584 counting only the distinct ones).

The product of its (nonzero) digits is 360, while the sum is 19.

The square root of 21331540 is about 4618.6080154090. The cubic root of 21331540 is about 277.3367380982.

Adding to 21331540 its reverse (4513312), we get a palindrome (25844852).

The spelling of 21331540 in words is "twenty-one million, three hundred thirty-one thousand, five hundred forty".