21315605 has 4 divisors (see below), whose sum is σ = 25578732. Its totient is φ = 17052480.

The previous prime is 21315599. The next prime is 21315607. The reversal of 21315605 is 50651312.

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 16589329 + 4726276 = 4073^2 + 2174^2 .

It is not a de Polignac number, because 21315605 - 2¹⁴ = 21299221 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21315607) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 2131556 + ... + 2131565.

It is an arithmetic number, because the mean of its divisors is an integer number (6394683).

Almost surely, 2^21315605 is an apocalyptic number.

It is an amenable number.

21315605 is a deficient number, since it is larger than the sum of its proper divisors (4263127).

21315605 is an equidigital number, since it uses as much as digits as its factorization.

21315605 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 4263126.

The product of its (nonzero) digits is 900, while the sum is 23.

The square root of 21315605 is about 4616.8826062615. The cubic root of 21315605 is about 277.2676625756.

Adding to 21315605 its reverse (50651312), we get a palindrome (71966917).

The spelling of 21315605 in words is "twenty-one million, three hundred fifteen thousand, six hundred five".