21605055 has 16 divisors (see below), whose sum is σ = 34631520. Its totient is φ = 11501568.

The previous prime is 21605053. The next prime is 21605057. The reversal of 21605055 is 55050612.

It is an interprime number because it is at equal distance from previous prime (21605053) and next prime (21605057).

It is not a de Polignac number, because 21605055 - 2¹ = 21605053 is a prime.

It is a plaindrome in base 16.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21605053) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 10599 + ... + 12471.

It is an arithmetic number, because the mean of its divisors is an integer number (2164470).

Almost surely, 2^21605055 is an apocalyptic number.

21605055 is a deficient number, since it is larger than the sum of its proper divisors (13026465).

21605055 is a wasteful number, since it uses less digits than its factorization.

21605055 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2650.

The product of its (nonzero) digits is 1500, while the sum is 24.

The square root of 21605055 is about 4648.1238150462. The cubic root of 21605055 is about 278.5170535366.

Adding to 21605055 its reverse (55050612), we get a palindrome (76655667).

The spelling of 21605055 in words is "twenty-one million, six hundred five thousand, fifty-five".