21305547 has 12 divisors (see below), whose sum is σ = 30853264. Its totient is φ = 14167440.

The previous prime is 21305533. The next prime is 21305551. The reversal of 21305547 is 74550312.

It is a happy number.

It is not a de Polignac number, because 21305547 - 2⁶ = 21305483 is a prime.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 21305547.

It is not an unprimeable number, because it can be changed into a prime (21305507) 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 11 ways as a sum of consecutive naturals, for example, 978 + ... + 6600.

Almost surely, 2^21305547 is an apocalyptic number.

21305547 is a deficient number, since it is larger than the sum of its proper divisors (9547717).

21305547 is a wasteful number, since it uses less digits than its factorization.

21305547 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 6050 (or 6047 counting only the distinct ones).

The product of its (nonzero) digits is 4200, while the sum is 27.

The square root of 21305547 is about 4615.7932146057. The cubic root of 21305547 is about 277.2240451272.

Adding to 21305547 its reverse (74550312), we get a palindrome (95855859).

The spelling of 21305547 in words is "twenty-one million, three hundred five thousand, five hundred forty-seven".