21520447 has 4 divisors (see below), whose sum is σ = 23175880. Its totient is φ = 19865016.

The previous prime is 21520441. The next prime is 21520451. The reversal of 21520447 is 74402512.

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

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21520447 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21520441) 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, 827697 + ... + 827722.

It is an arithmetic number, because the mean of its divisors is an integer number (5793970).

Almost surely, 2^21520447 is an apocalyptic number.

21520447 is a deficient number, since it is larger than the sum of its proper divisors (1655433).

21520447 is a wasteful number, since it uses less digits than its factorization.

21520447 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1655432.

The product of its (nonzero) digits is 2240, while the sum is 25.

The square root of 21520447 is about 4639.0135804932. The cubic root of 21520447 is about 278.1530091221.

Adding to 21520447 its reverse (74402512), we get a palindrome (95922959).

The spelling of 21520447 in words is "twenty-one million, five hundred twenty thousand, four hundred forty-seven".