21006447 has 36 divisors (see below), whose sum is σ = 35842968. Its totient is φ = 10903200.

The previous prime is 21006439. The next prime is 21006451. The reversal of 21006447 is 74460012.

It is not a de Polignac number, because 21006447 - 2³ = 21006439 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21006487) by changing a digit.

It is a polite number, since it can be written in 35 ways as a sum of consecutive naturals, for example, 17197 + ... + 18377.

It is an arithmetic number, because the mean of its divisors is an integer number (995638).

Almost surely, 2^21006447 is an apocalyptic number.

21006447 is a deficient number, since it is larger than the sum of its proper divisors (14836521).

21006447 is a wasteful number, since it uses less digits than its factorization.

21006447 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1220 (or 1202 counting only the distinct ones).

The product of its (nonzero) digits is 1344, while the sum is 24.

The square root of 21006447 is about 4583.2790663454. The cubic root of 21006447 is about 275.9206477402.

Adding to 21006447 its reverse (74460012), we get a palindrome (95466459).

The spelling of 21006447 in words is "twenty-one million, six thousand, four hundred forty-seven".