21908421 has 16 divisors (see below), whose sum is σ = 32643520. Its totient is φ = 14521680.

The previous prime is 21908407. The next prime is 21908423. The reversal of 21908421 is 12480912.

It is not a de Polignac number, because 21908421 - 2⁹ = 21907909 is a prime.

It is a Harshad number since it is a multiple of its sum of digits (27).

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21908423) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 2646 + ... + 7128.

It is an arithmetic number, because the mean of its divisors is an integer number (2040220).

Almost surely, 2^21908421 is an apocalyptic number.

It is an amenable number.

21908421 is a deficient number, since it is larger than the sum of its proper divisors (10735099).

21908421 is a wasteful number, since it uses less digits than its factorization.

21908421 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 4673 (or 4667 counting only the distinct ones).

The product of its (nonzero) digits is 1152, while the sum is 27.

The square root of 21908421 is about 4680.6432250279. The cubic root of 21908421 is about 279.8145923918.

The spelling of 21908421 in words is "twenty-one million, nine hundred eight thousand, four hundred twenty-one".