21571247 has 4 divisors (see below), whose sum is σ = 21924936. Its totient is φ = 21217560.

The previous prime is 21571243. The next prime is 21571267. The reversal of 21571247 is 74217512.

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 21571247 - 2² = 21571243 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 (21571241) 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, 176753 + ... + 176874.

It is an arithmetic number, because the mean of its divisors is an integer number (5481234).

Almost surely, 2^21571247 is an apocalyptic number.

21571247 is a deficient number, since it is larger than the sum of its proper divisors (353689).

21571247 is an equidigital number, since it uses as much as digits as its factorization.

21571247 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 353688.

The product of its digits is 3920, while the sum is 29.

The square root of 21571247 is about 4644.4856550537. The cubic root of 21571247 is about 278.3717014370.

Adding to 21571247 its reverse (74217512), we get a palindrome (95788759).

The spelling of 21571247 in words is "twenty-one million, five hundred seventy-one thousand, two hundred forty-seven".