21020040 has 64 divisors (see below), whose sum is σ = 70070400. Its totient is φ = 5605056.

The previous prime is 21020039. The next prime is 21020053. The reversal of 21020040 is 4002012.

It is a Harshad number since it is a multiple of its sum of digits (9).

It is an unprimeable number.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 8652 + ... + 10811.

It is an arithmetic number, because the mean of its divisors is an integer number (1094850).

Almost surely, 2^21020040 is an apocalyptic number.

21020040 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21020040 is an abundant number, since it is smaller than the sum of its proper divisors (49050360).

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

21020040 is a wasteful number, since it uses less digits than its factorization.

21020040 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 19483 (or 19473 counting only the distinct ones).

The product of its (nonzero) digits is 16, while the sum is 9.

The square root of 21020040 is about 4584.7617168180. The cubic root of 21020040 is about 275.9801498011.

Adding to 21020040 its reverse (4002012), we get a palindrome (25022052).

The spelling of 21020040 in words is "twenty-one million, twenty thousand, forty".