21605505 has 16 divisors (see below), whose sum is σ = 35156160. Its totient is φ = 11327168.

The previous prime is 21605501. The next prime is 21605509. The reversal of 21605505 is 50550612.

It is an interprime number because it is at equal distance from previous prime (21605501) and next prime (21605509).

It is a cyclic number.

It is not a de Polignac number, because 21605505 - 2² = 21605501 is a prime.

It is a Curzon number.

It is not an unprimeable number, because it can be changed into a prime (21605501) 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, 11322 + ... + 13091.

It is an arithmetic number, because the mean of its divisors is an integer number (2197260).

Almost surely, 2^21605505 is an apocalyptic number.

It is an amenable number.

21605505 is a deficient number, since it is larger than the sum of its proper divisors (13550655).

21605505 is a wasteful number, since it uses less digits than its factorization.

21605505 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 24480.

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

The square root of 21605505 is about 4648.1722214221. The cubic root of 21605505 is about 278.5189872169.

The spelling of 21605505 in words is "twenty-one million, six hundred five thousand, five hundred five".