21155605 has 4 divisors (see below), whose sum is σ = 25386732. Its totient is φ = 16924480.

The previous prime is 21155591. The next prime is 21155611. The reversal of 21155605 is 50655112.

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 10093329 + 11062276 = 3177^2 + 3326^2 .

It is a de Polignac number, because none of the positive numbers 2^k-21155605 is a prime.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 21155605.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 2115556 + ... + 2115565.

It is an arithmetic number, because the mean of its divisors is an integer number (6346683).

Almost surely, 2^21155605 is an apocalyptic number.

It is an amenable number.

21155605 is a deficient number, since it is larger than the sum of its proper divisors (4231127).

21155605 is an equidigital number, since it uses as much as digits as its factorization.

21155605 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 4231126.

The product of its (nonzero) digits is 1500, while the sum is 25.

The square root of 21155605 is about 4599.5222578003. The cubic root of 21155605 is about 276.5721738240.

The spelling of 21155605 in words is "twenty-one million, one hundred fifty-five thousand, six hundred five".