21021008 has 10 divisors (see below), whose sum is σ = 40728234. Its totient is φ = 10510496.

The previous prime is 21021001. The next prime is 21021043. The reversal of 21021008 is 80012012.

It can be written as a sum of positive squares in only one way, i.e., 20720704 + 300304 = 4552^2 + 548^2 .

It is a junction number, because it is equal to n+sod(n) for n = 21020983 and 21021001.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21021001) 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 as a sum of consecutive naturals, namely, 656891 + ... + 656922.

Almost surely, 2^21021008 is an apocalyptic number.

It is an amenable number.

21021008 is a deficient number, since it is larger than the sum of its proper divisors (19707226).

21021008 is a wasteful number, since it uses less digits than its factorization.

21021008 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1313821 (or 1313815 counting only the distinct ones).

The product of its (nonzero) digits is 32, while the sum is 14.

The square root of 21021008 is about 4584.8672827030. The cubic root of 21021008 is about 275.9843861502.

The spelling of 21021008 in words is "twenty-one million, twenty-one thousand, eight".