21131647 has 4 divisors (see below), whose sum is σ = 21186360. Its totient is φ = 21076936.

The previous prime is 21131597. The next prime is 21131651. The reversal of 21131647 is 74613112.

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 21131647 - 2⁷ = 21131519 is a prime.

It is a super-3 number, since 3×21131647³ (a number of 23 digits) contains 333 as substring.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21131147) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 26773 + ... + 27550.

It is an arithmetic number, because the mean of its divisors is an integer number (5296590).

Almost surely, 2^21131647 is an apocalyptic number.

21131647 is a deficient number, since it is larger than the sum of its proper divisors (54713).

21131647 is an equidigital number, since it uses as much as digits as its factorization.

21131647 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 54712.

The product of its digits is 1008, while the sum is 25.

The square root of 21131647 is about 4596.9171191136. The cubic root of 21131647 is about 276.4677315419.

Adding to 21131647 its reverse (74613112), we get a palindrome (95744759).

The spelling of 21131647 in words is "twenty-one million, one hundred thirty-one thousand, six hundred forty-seven".