21003545 has 4 divisors (see below), whose sum is σ = 25204260. Its totient is φ = 16802832.

The previous prime is 21003539. The next prime is 21003547. The reversal of 21003545 is 54530012.

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 13756681 + 7246864 = 3709^2 + 2692^2 .

It is a cyclic number.

It is not a de Polignac number, because 21003545 - 2¹⁰ = 21002521 is a prime.

It is a super-2 number, since 2×21003545² = 882297805134050, which contains 22 as substring.

It is not an unprimeable number, because it can be changed into a prime (21003547) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 2100350 + ... + 2100359.

It is an arithmetic number, because the mean of its divisors is an integer number (6301065).

Almost surely, 2^21003545 is an apocalyptic number.

It is an amenable number.

21003545 is a deficient number, since it is larger than the sum of its proper divisors (4200715).

21003545 is an equidigital number, since it uses as much as digits as its factorization.

21003545 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 4200714.

The product of its (nonzero) digits is 600, while the sum is 20.

The square root of 21003545 is about 4582.9624698442. The cubic root of 21003545 is about 275.9079411872.

Adding to 21003545 its reverse (54530012), we get a palindrome (75533557).

The spelling of 21003545 in words is "twenty-one million, three thousand, five hundred forty-five".