21115605 has 16 divisors (see below), whose sum is σ = 38611584. Its totient is φ = 9652800.

The previous prime is 21115603. The next prime is 21115651. The reversal of 21115605 is 50651112.

It is not a de Polignac number, because 21115605 - 2¹ = 21115603 is a prime.

It is a Harshad number since it is a multiple of its sum of digits (21).

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21115603) by changing a digit.

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 15 ways as a sum of consecutive naturals, for example, 100446 + ... + 100655.

It is an arithmetic number, because the mean of its divisors is an integer number (2413224).

Almost surely, 2^21115605 is an apocalyptic number.

It is an amenable number.

21115605 is a deficient number, since it is larger than the sum of its proper divisors (17495979).

21115605 is a wasteful number, since it uses less digits than its factorization.

21115605 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 201116.

The product of its (nonzero) digits is 300, while the sum is 21.

The square root of 21115605 is about 4595.1719227903. The cubic root of 21115605 is about 276.3977540634.

Adding to 21115605 its reverse (50651112), we get a palindrome (71766717).

The spelling of 21115605 in words is "twenty-one million, one hundred fifteen thousand, six hundred five".