21605659 has 2 divisors, whose sum is σ = 21605660. Its totient is φ = 21605658.

The previous prime is 21605627. The next prime is 21605663. The reversal of 21605659 is 95650612.

It is a happy number.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 21605659 - 2⁵ = 21605627 is a prime.

It is not a weakly prime, because it can be changed into another prime (21605159) 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, 10802829 + 10802830.

It is an arithmetic number, because the mean of its divisors is an integer number (10802830).

Almost surely, 2^21605659 is an apocalyptic number.

21605659 is a deficient number, since it is larger than the sum of its proper divisors (1).

21605659 is an equidigital number, since it uses as much as digits as its factorization.

21605659 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 16200, while the sum is 34.

The square root of 21605659 is about 4648.1887870438. The cubic root of 21605659 is about 278.5196489590.

The spelling of 21605659 in words is "twenty-one million, six hundred five thousand, six hundred fifty-nine".