21420405 has 12 divisors (see below), whose sum is σ = 37128780. Its totient is φ = 11424192.

The previous prime is 21420403. The next prime is 21420433. The reversal of 21420405 is 50402412.

It can be written as a sum of positive squares in 2 ways, for example, as 4626801 + 16793604 = 2151^2 + 4098^2 .

It is not a de Polignac number, because 21420405 - 2¹ = 21420403 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21420403) by changing a digit.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 237960 + ... + 238049.

It is an arithmetic number, because the mean of its divisors is an integer number (3094065).

Almost surely, 2^21420405 is an apocalyptic number.

It is an amenable number.

21420405 is a deficient number, since it is larger than the sum of its proper divisors (15708375).

21420405 is a wasteful number, since it uses less digits than its factorization.

21420405 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 476020 (or 476017 counting only the distinct ones).

The product of its (nonzero) digits is 320, while the sum is 18.

The square root of 21420405 is about 4628.2183397070. The cubic root of 21420405 is about 277.7213233124.

Adding to 21420405 its reverse (50402412), we get a palindrome (71822817).

The spelling of 21420405 in words is "twenty-one million, four hundred twenty thousand, four hundred five".