21505005 has 24 divisors (see below), whose sum is σ = 37459968. Its totient is φ = 11412576.

The previous prime is 21504971. The next prime is 21505007. The reversal of 21505005 is 50050512.

It is not a de Polignac number, because 21505005 - 2⁷ = 21504877 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21505007) by changing a digit.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 8964 + ... + 11106.

It is an arithmetic number, because the mean of its divisors is an integer number (1560832).

Almost surely, 2^21505005 is an apocalyptic number.

It is an amenable number.

21505005 is a deficient number, since it is larger than the sum of its proper divisors (15954963).

21505005 is a wasteful number, since it uses less digits than its factorization.

21505005 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2377 (or 2374 counting only the distinct ones).

The product of its (nonzero) digits is 250, while the sum is 18.

The square root of 21505005 is about 4637.3489193719. The cubic root of 21505005 is about 278.0864636251.

Adding to 21505005 its reverse (50050512), we get a palindrome (71555517).

The spelling of 21505005 in words is "twenty-one million, five hundred five thousand, five".