21042047 has 4 divisors (see below), whose sum is σ = 22660680. Its totient is φ = 19423416.

The previous prime is 21042017. The next prime is 21042053. The reversal of 21042047 is 74024012.

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

It is a cyclic number.

It is not a de Polignac number, because 21042047 - 2⁶ = 21041983 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21042017) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 809297 + ... + 809322.

It is an arithmetic number, because the mean of its divisors is an integer number (5665170).

Almost surely, 2^21042047 is an apocalyptic number.

21042047 is a deficient number, since it is larger than the sum of its proper divisors (1618633).

21042047 is a wasteful number, since it uses less digits than its factorization.

21042047 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1618632.

The product of its (nonzero) digits is 448, while the sum is 20.

The square root of 21042047 is about 4587.1611046485. The cubic root of 21042047 is about 276.0764289841.

Adding to 21042047 its reverse (74024012), we get a palindrome (95066059).

The spelling of 21042047 in words is "twenty-one million, forty-two thousand, forty-seven".