21031540 has 48 divisors (see below), whose sum is σ = 45983952. Its totient is φ = 8073216.

The previous prime is 21031531. The next prime is 21031559. The reversal of 21031540 is 4513012.

It can be written as a sum of positive squares in 8 ways, for example, as 3290596 + 17740944 = 1814^2 + 4212^2 .

It is a congruent number.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 71634 + ... + 71926.

It is an arithmetic number, because the mean of its divisors is an integer number (957999).

Almost surely, 2^21031540 is an apocalyptic number.

21031540 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21031540, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (22991976).

21031540 is an abundant number, since it is smaller than the sum of its proper divisors (24952412).

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

21031540 is a wasteful number, since it uses less digits than its factorization.

21031540 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 436 (or 434 counting only the distinct ones).

The product of its (nonzero) digits is 120, while the sum is 16.

The square root of 21031540 is about 4586.0156999295. The cubic root of 21031540 is about 276.0304699260.

Adding to 21031540 its reverse (4513012), we get a palindrome (25544552).

The spelling of 21031540 in words is "twenty-one million, thirty-one thousand, five hundred forty".