21505211 has 24 divisors (see below), whose sum is σ = 27509664. Its totient is φ = 16369920.

The previous prime is 21505199. The next prime is 21505219. The reversal of 21505211 is 11250512.

It is not a de Polignac number, because 21505211 - 2¹⁴ = 21488827 is a prime.

It is a self number, because there is not a number n which added to its sum of digits gives 21505211.

It is not an unprimeable number, because it can be changed into a prime (21505219) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 76391 + ... + 76671.

It is an arithmetic number, because the mean of its divisors is an integer number (1146236).

Almost surely, 2^21505211 is an apocalyptic number.

21505211 is a deficient number, since it is larger than the sum of its proper divisors (6004453).

21505211 is a wasteful number, since it uses less digits than its factorization.

21505211 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 359 (or 330 counting only the distinct ones).

The product of its (nonzero) digits is 100, while the sum is 17.

The square root of 21505211 is about 4637.3711302849. The cubic root of 21505211 is about 278.0873515677.

Adding to 21505211 its reverse (11250512), we get a palindrome (32755723).

The spelling of 21505211 in words is "twenty-one million, five hundred five thousand, two hundred eleven".