21005503 has 2 divisors, whose sum is σ = 21005504. Its totient is φ = 21005502.

The previous prime is 21005477. The next prime is 21005539. The reversal of 21005503 is 30550012.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 21005503 - 2¹³ = 20997311 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21005903) 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 as a sum of consecutive naturals, namely, 10502751 + 10502752.

It is an arithmetic number, because the mean of its divisors is an integer number (10502752).

Almost surely, 2^21005503 is an apocalyptic number.

21005503 is a deficient number, since it is larger than the sum of its proper divisors (1).

21005503 is an equidigital number, since it uses as much as digits as its factorization.

21005503 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 150, while the sum is 16.

The square root of 21005503 is about 4583.1760821509. The cubic root of 21005503 is about 275.9165145171.

Adding to 21005503 its reverse (30550012), we get a palindrome (51555515).

The spelling of 21005503 in words is "twenty-one million, five thousand, five hundred three".