21121405 has 4 divisors (see below), whose sum is σ = 25345692. Its totient is φ = 16897120.

The previous prime is 21121403. The next prime is 21121411. The reversal of 21121405 is 50412112.

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 2965284 + 18156121 = 1722^2 + 4261^2 .

It is not a de Polignac number, because 21121405 - 2¹ = 21121403 is a prime.

It is a super-2 number, since 2×21121405² = 892227498348050, which contains 22 as substring.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21121403) 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, 2112136 + ... + 2112145.

It is an arithmetic number, because the mean of its divisors is an integer number (6336423).

Almost surely, 2^21121405 is an apocalyptic number.

It is an amenable number.

21121405 is a deficient number, since it is larger than the sum of its proper divisors (4224287).

21121405 is an equidigital number, since it uses as much as digits as its factorization.

21121405 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 4224286.

The product of its (nonzero) digits is 80, while the sum is 16.

The square root of 21121405 is about 4595.8029766299. The cubic root of 21121405 is about 276.4230585750.

Adding to 21121405 its reverse (50412112), we get a palindrome (71533517).

The spelling of 21121405 in words is "twenty-one million, one hundred twenty-one thousand, four hundred five".