21015040 has 40 divisors (see below), whose sum is σ = 50392980. Its totient is φ = 8404992.

The previous prime is 21015023. The next prime is 21015041. The reversal of 21015040 is 4051012.

It can be written as a sum of positive squares in 2 ways, for example, as 18800896 + 2214144 = 4336^2 + 1488^2 .

It is a tau number, because it is divible by the number of its divisors (40).

It is a zygodrome in base 4.

It is a self number, because there is not a number n which added to its sum of digits gives 21015040.

It is not an unprimeable number, because it can be changed into a prime (21015041) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 1545 + ... + 6664.

Almost surely, 2^21015040 is an apocalyptic number.

21015040 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21015040 is an abundant number, since it is smaller than the sum of its proper divisors (29377940).

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

21015040 is an frugal number, since it uses more digits than its factorization.

21015040 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 8232 (or 8216 counting only the distinct ones).

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

The square root of 21015040 is about 4584.2163997787. The cubic root of 21015040 is about 275.9582657613.

Adding to 21015040 its reverse (4051012), we get a palindrome (25066052).

The spelling of 21015040 in words is "twenty-one million, fifteen thousand, forty".