21008421 has 36 divisors (see below), whose sum is σ = 35938656. Its totient is φ = 11584080.

The previous prime is 21008419. The next prime is 21008423. The reversal of 21008421 is 12480012.

It is an interprime number because it is at equal distance from previous prime (21008419) and next prime (21008423).

It is not a de Polignac number, because 21008421 - 2¹ = 21008419 is a prime.

It is a junction number, because it is equal to n+sod(n) for n = 21008394 and 21008403.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21008423) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (7) of ones.

It is a polite number, since it can be written in 35 ways as a sum of consecutive naturals, for example, 60370 + ... + 60716.

It is an arithmetic number, because the mean of its divisors is an integer number (998296).

Almost surely, 2^21008421 is an apocalyptic number.

21008421 is a gapful number since it is divisible by the number (21) formed by its first and last digit.

It is an amenable number.

21008421 is a deficient number, since it is larger than the sum of its proper divisors (14930235).

21008421 is a wasteful number, since it uses less digits than its factorization.

21008421 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 422 (or 388 counting only the distinct ones).

The product of its (nonzero) digits is 128, while the sum is 18.

The square root of 21008421 is about 4583.4944092908. The cubic root of 21008421 is about 275.9292903297.

Adding to 21008421 its reverse (12480012), we get a palindrome (33488433).

The spelling of 21008421 in words is "twenty-one million, eight thousand, four hundred twenty-one".