21806647 has 2 divisors, whose sum is σ = 21806648. Its totient is φ = 21806646.

The previous prime is 21806641. The next prime is 21806657. The reversal of 21806647 is 74660812.

It is a weak prime.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21806647 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21806641) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10903323 + 10903324.

It is an arithmetic number, because the mean of its divisors is an integer number (10903324).

Almost surely, 2^21806647 is an apocalyptic number.

21806647 is a deficient number, since it is larger than the sum of its proper divisors (1).

21806647 is an equidigital number, since it uses as much as digits as its factorization.

21806647 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 16128, while the sum is 34.

The square root of 21806647 is about 4669.7587732130. The cubic root of 21806647 is about 279.3806335082.

The spelling of 21806647 in words is "twenty-one million, eight hundred six thousand, six hundred forty-seven".