21081647 has 2 divisors, whose sum is σ = 21081648. Its totient is φ = 21081646.

The previous prime is 21081631. The next prime is 21081673. The reversal of 21081647 is 74618012.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 21081647 - 2⁴ = 21081631 is a prime.

It is a Chen prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21081947) 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 as a sum of consecutive naturals, namely, 10540823 + 10540824.

It is an arithmetic number, because the mean of its divisors is an integer number (10540824).

Almost surely, 2^21081647 is an apocalyptic number.

21081647 is a deficient number, since it is larger than the sum of its proper divisors (1).

21081647 is an equidigital number, since it uses as much as digits as its factorization.

21081647 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 2688, while the sum is 29.

The square root of 21081647 is about 4591.4754709135. The cubic root of 21081647 is about 276.2495074485.

Adding to 21081647 its reverse (74618012), we get a palindrome (95699659).

The spelling of 21081647 in words is "twenty-one million, eighty-one thousand, six hundred forty-seven".