21001540 has 24 divisors (see below), whose sum is σ = 50404032. Its totient is φ = 7200480.

The previous prime is 21001531. The next prime is 21001549. The reversal of 21001540 is 4510012.

It is an interprime number because it is at equal distance from previous prime (21001531) and next prime (21001549).

It is a self number, because there is not a number n which added to its sum of digits gives 21001540.

It is not an unprimeable number, because it can be changed into a prime (21001549) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 74866 + ... + 75145.

It is an arithmetic number, because the mean of its divisors is an integer number (2100168).

Almost surely, 2^21001540 is an apocalyptic number.

21001540 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21001540 is an abundant number, since it is smaller than the sum of its proper divisors (29402492).

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

21001540 is a wasteful number, since it uses less digits than its factorization.

21001540 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 150027 (or 150025 counting only the distinct ones).

The product of its (nonzero) digits is 40, while the sum is 13.

The square root of 21001540 is about 4582.7437196509. The cubic root of 21001540 is about 275.8991615101.

Adding to 21001540 its reverse (4510012), we get a palindrome (25511552).

The spelling of 21001540 in words is "twenty-one million, one thousand, five hundred forty".