21000545 has 4 divisors (see below), whose sum is σ = 25200660. Its totient is φ = 16800432.

The previous prime is 21000533. The next prime is 21000557. The reversal of 21000545 is 54500012.

It is a semiprime because it is the product of two primes.

It is an interprime number because it is at equal distance from previous prime (21000533) and next prime (21000557).

It can be written as a sum of positive squares in 2 ways, for example, as 5326864 + 15673681 = 2308^2 + 3959^2 .

It is a cyclic number.

It is not a de Polignac number, because 21000545 - 2⁶ = 21000481 is a prime.

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, 2100050 + ... + 2100059.

It is an arithmetic number, because the mean of its divisors is an integer number (6300165).

Almost surely, 2^21000545 is an apocalyptic number.

It is an amenable number.

21000545 is a deficient number, since it is larger than the sum of its proper divisors (4200115).

21000545 is an equidigital number, since it uses as much as digits as its factorization.

21000545 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 4200114.

The product of its (nonzero) digits is 200, while the sum is 17.

The square root of 21000545 is about 4582.6351589451. The cubic root of 21000545 is about 275.8948043058.

Adding to 21000545 its reverse (54500012), we get a palindrome (75500557).

The spelling of 21000545 in words is "twenty-one million, five hundred forty-five", and thus it is an aban number.