21005445 has 32 divisors (see below), whose sum is σ = 35020800. Its totient is φ = 10739520.

The previous prime is 21005441. The next prime is 21005473. The reversal of 21005445 is 54450012.

It is not a de Polignac number, because 21005445 - 2² = 21005441 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21005441) 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 31 ways as a sum of consecutive naturals, for example, 92422 + ... + 92648.

It is an arithmetic number, because the mean of its divisors is an integer number (1094400).

Almost surely, 2^21005445 is an apocalyptic number.

It is an amenable number.

21005445 is a deficient number, since it is larger than the sum of its proper divisors (14015355).

21005445 is a wasteful number, since it uses less digits than its factorization.

21005445 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 465.

The product of its (nonzero) digits is 800, while the sum is 21.

The square root of 21005445 is about 4583.1697546567. The cubic root of 21005445 is about 275.9162605650.

Adding to 21005445 its reverse (54450012), we get a palindrome (75455457).

The spelling of 21005445 in words is "twenty-one million, five thousand, four hundred forty-five".