21506647 has 2 divisors, whose sum is σ = 21506648. Its totient is φ = 21506646.

The previous prime is 21506629. The next prime is 21506659. The reversal of 21506647 is 74660512.

It is a happy number.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 21506647 - 2⁷ = 21506519 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21506627) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10753323 + 10753324.

It is an arithmetic number, because the mean of its divisors is an integer number (10753324).

Almost surely, 2^21506647 is an apocalyptic number.

21506647 is a deficient number, since it is larger than the sum of its proper divisors (1).

21506647 is an equidigital number, since it uses as much as digits as its factorization.

21506647 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 10080, while the sum is 31.

The square root of 21506647 is about 4637.5259568007. The cubic root of 21506647 is about 278.0935411458.

The spelling of 21506647 in words is "twenty-one million, five hundred six thousand, six hundred forty-seven".