21345405 has 16 divisors (see below), whose sum is σ = 34586880. Its totient is φ = 11239488.

The previous prime is 21345397. The next prime is 21345409. The reversal of 21345405 is 50454312.

It is not a de Polignac number, because 21345405 - 2³ = 21345397 is a prime.

It is a super-2 number, since 2×21345405² = 911252629228050, which contains 22 as substring.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21345409) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 7822 + ... + 10191.

It is an arithmetic number, because the mean of its divisors is an integer number (2161680).

Almost surely, 2^21345405 is an apocalyptic number.

It is an amenable number.

21345405 is a deficient number, since it is larger than the sum of its proper divisors (13241475).

21345405 is a wasteful number, since it uses less digits than its factorization.

21345405 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 18100.

The product of its (nonzero) digits is 2400, while the sum is 24.

The square root of 21345405 is about 4620.1087649535. The cubic root of 21345405 is about 277.3968125398.

Adding to 21345405 its reverse (50454312), we get a palindrome (71799717).

The spelling of 21345405 in words is "twenty-one million, three hundred forty-five thousand, four hundred five".