21208621 has 12 divisors (see below), whose sum is σ = 24788160. Its totient is φ = 18092760.

The previous prime is 21208613. The next prime is 21208633. The reversal of 21208621 is 12680212.

It is not a de Polignac number, because 21208621 - 2³ = 21208613 is a prime.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 21208592 and 21208601.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21208601) 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 11 ways as a sum of consecutive naturals, for example, 10806 + ... + 12616.

It is an arithmetic number, because the mean of its divisors is an integer number (2065680).

Almost surely, 2^21208621 is an apocalyptic number.

It is an amenable number.

21208621 is a deficient number, since it is larger than the sum of its proper divisors (3579539).

21208621 is a wasteful number, since it uses less digits than its factorization.

21208621 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2064 (or 2057 counting only the distinct ones).

The product of its (nonzero) digits is 384, while the sum is 22.

The square root of 21208621 is about 4605.2818589094. The cubic root of 21208621 is about 276.8030112954.

Adding to 21208621 its reverse (12680212), we get a palindrome (33888833).

The spelling of 21208621 in words is "twenty-one million, two hundred eight thousand, six hundred twenty-one".