21609505 has 4 divisors (see below), whose sum is σ = 25931412. Its totient is φ = 17287600.

The previous prime is 21609487. The next prime is 21609527. The reversal of 21609505 is 50590612.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 13808656 + 7800849 = 3716^2 + 2793^2 .

It is not a de Polignac number, because 21609505 - 2⁵ = 21609473 is a prime.

It is a Duffinian number.

It is an unprimeable number.

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 3 ways as a sum of consecutive naturals, for example, 2160946 + ... + 2160955.

It is an arithmetic number, because the mean of its divisors is an integer number (6482853).

Almost surely, 2^21609505 is an apocalyptic number.

It is an amenable number.

21609505 is a deficient number, since it is larger than the sum of its proper divisors (4321907).

21609505 is an equidigital number, since it uses as much as digits as its factorization.

21609505 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 4321906.

The product of its (nonzero) digits is 2700, while the sum is 28.

The square root of 21609505 is about 4648.6024781648. The cubic root of 21609505 is about 278.5361743057.

The spelling of 21609505 in words is "twenty-one million, six hundred nine thousand, five hundred five".