21005648 has 10 divisors (see below), whose sum is σ = 40698474. Its totient is φ = 10502816.

The previous prime is 21005627. The next prime is 21005651. The reversal of 21005648 is 84650012.

It can be written as a sum of positive squares in only one way, i.e., 18731584 + 2274064 = 4328^2 + 1508^2 .

It is a congruent number.

It is an unprimeable number.

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, 656411 + ... + 656442.

Almost surely, 2^21005648 is an apocalyptic number.

It is an amenable number.

21005648 is a deficient number, since it is larger than the sum of its proper divisors (19692826).

21005648 is a wasteful number, since it uses less digits than its factorization.

21005648 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1312861 (or 1312855 counting only the distinct ones).

The product of its (nonzero) digits is 1920, while the sum is 26.

The square root of 21005648 is about 4583.1919008481. The cubic root of 21005648 is about 275.9171493952.

The spelling of 21005648 in words is "twenty-one million, five thousand, six hundred forty-eight".