21145645 has 4 divisors (see below), whose sum is σ = 25374780. Its totient is φ = 16916512.

The previous prime is 21145639. The next prime is 21145667. The reversal of 21145645 is 54654112.

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 11329956 + 9815689 = 3366^2 + 3133^2 .

It is a cyclic number.

It is not a de Polignac number, because 21145645 - 2¹³ = 21137453 is a prime.

It is a super-3 number, since 3×21145645³ (a number of 23 digits) contains 333 as substring.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 2114560 + ... + 2114569.

It is an arithmetic number, because the mean of its divisors is an integer number (6343695).

Almost surely, 2^21145645 is an apocalyptic number.

It is an amenable number.

21145645 is a deficient number, since it is larger than the sum of its proper divisors (4229135).

21145645 is an equidigital number, since it uses as much as digits as its factorization.

21145645 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 4229134.

The product of its digits is 4800, while the sum is 28.

The square root of 21145645 is about 4598.4394091909. The cubic root of 21145645 is about 276.5287638741.

Adding to 21145645 its reverse (54654112), we get a palindrome (75799757).

The spelling of 21145645 in words is "twenty-one million, one hundred forty-five thousand, six hundred forty-five".