21008424 has 32 divisors (see below), whose sum is σ = 53745120. Its totient is φ = 6839616.

The previous prime is 21008423. The next prime is 21008459. The reversal of 21008424 is 42480012.

It is a self number, because there is not a number n which added to its sum of digits gives 21008424.

It is not an unprimeable number, because it can be changed into a prime (21008423) 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, 9147 + ... + 11210.

It is an arithmetic number, because the mean of its divisors is an integer number (1679535).

Almost surely, 2^21008424 is an apocalyptic number.

21008424 is a gapful number since it is divisible by the number (24) formed by its first and last digit.

It is an amenable number.

21008424 is an abundant number, since it is smaller than the sum of its proper divisors (32736696).

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

21008424 is a wasteful number, since it uses less digits than its factorization.

21008424 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 20409 (or 20405 counting only the distinct ones).

The product of its (nonzero) digits is 512, while the sum is 21.

The square root of 21008424 is about 4583.4947365520. The cubic root of 21008424 is about 275.9293034639.

Adding to 21008424 its reverse (42480012), we get a palindrome (63488436).

The spelling of 21008424 in words is "twenty-one million, eight thousand, four hundred twenty-four".