21305105 has 4 divisors (see below), whose sum is σ = 25566132. Its totient is φ = 17044080.

The previous prime is 21305101. The next prime is 21305113. The reversal of 21305105 is 50150312.

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 6436369 + 14868736 = 2537^2 + 3856^2 .

It is not a de Polignac number, because 21305105 - 2² = 21305101 is a prime.

It is a super-2 number, since 2×21305105² = 907814998122050, which contains 22 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21305101) 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, 2130506 + ... + 2130515.

It is an arithmetic number, because the mean of its divisors is an integer number (6391533).

Almost surely, 2^21305105 is an apocalyptic number.

It is an amenable number.

21305105 is a deficient number, since it is larger than the sum of its proper divisors (4261027).

21305105 is an equidigital number, since it uses as much as digits as its factorization.

21305105 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 4261026.

The product of its (nonzero) digits is 150, while the sum is 17.

The square root of 21305105 is about 4615.7453352628. The cubic root of 21305105 is about 277.2221280384. Note that the first 3 decimals are identical.

Adding to 21305105 its reverse (50150312), we get a palindrome (71455417).

The spelling of 21305105 in words is "twenty-one million, three hundred five thousand, one hundred five".