21505055 has 32 divisors (see below), whose sum is σ = 31933440. Its totient is φ = 13668480.

The previous prime is 21505039. The next prime is 21505063. The reversal of 21505055 is 55050512.

It is not a de Polignac number, because 21505055 - 2⁴ = 21505039 is a prime.

It is a self number, because there is not a number n which added to its sum of digits gives 21505055.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 31 ways as a sum of consecutive naturals, for example, 12794 + ... + 14376.

It is an arithmetic number, because the mean of its divisors is an integer number (997920).

Almost surely, 2^21505055 is an apocalyptic number.

21505055 is a deficient number, since it is larger than the sum of its proper divisors (10428385).

21505055 is a wasteful number, since it uses less digits than its factorization.

21505055 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1631.

The product of its (nonzero) digits is 1250, while the sum is 23.

The square root of 21505055 is about 4637.3543103800. The cubic root of 21505055 is about 278.0866791457.

Adding to 21505055 its reverse (55050512), we get a palindrome (76555567).

The spelling of 21505055 in words is "twenty-one million, five hundred five thousand, fifty-five".