21042505 has 12 divisors (see below), whose sum is σ = 27756036. Its totient is φ = 15303200.

The previous prime is 21042491. The next prime is 21042533. The reversal of 21042505 is 50524012.

It can be written as a sum of positive squares in 2 ways, for example, as 7382089 + 13660416 = 2717^2 + 3696^2 .

It is not a de Polignac number, because 21042505 - 2⁵ = 21042473 is a prime.

It is an unprimeable number.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 16786 + ... + 17995.

It is an arithmetic number, because the mean of its divisors is an integer number (2313003).

Almost surely, 2^21042505 is an apocalyptic number.

It is an amenable number.

21042505 is a deficient number, since it is larger than the sum of its proper divisors (6713531).

21042505 is a wasteful number, since it uses less digits than its factorization.

21042505 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 34808 (or 34797 counting only the distinct ones).

The product of its (nonzero) digits is 400, while the sum is 19.

The square root of 21042505 is about 4587.2110263209. The cubic root of 21042505 is about 276.0784319909.

Adding to 21042505 its reverse (50524012), we get a palindrome (71566517).

The spelling of 21042505 in words is "twenty-one million, forty-two thousand, five hundred five".