21905647 has 2 divisors, whose sum is σ = 21905648. Its totient is φ = 21905646.

The previous prime is 21905641. The next prime is 21905687. The reversal of 21905647 is 74650912.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 21905647 - 2⁷ = 21905519 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21905641) 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, 10952823 + 10952824.

It is an arithmetic number, because the mean of its divisors is an integer number (10952824).

Almost surely, 2^21905647 is an apocalyptic number.

21905647 is a deficient number, since it is larger than the sum of its proper divisors (1).

21905647 is an equidigital number, since it uses as much as digits as its factorization.

21905647 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 15120, while the sum is 34.

The square root of 21905647 is about 4680.3468888534. The cubic root of 21905647 is about 279.8027820405.

The spelling of 21905647 in words is "twenty-one million, nine hundred five thousand, six hundred forty-seven".