21665689 has 2 divisors, whose sum is σ = 21665690. Its totient is φ = 21665688.

The previous prime is 21665653. The next prime is 21665713. The reversal of 21665689 is 98656612.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 18662400 + 3003289 = 4320^2 + 1733^2 .

It is a cyclic number.

It is not a de Polignac number, because 21665689 - 2¹³ = 21657497 is a prime.

It is a super-3 number, since 3×21665689³ (a number of 23 digits) contains 333 as substring.

It is not a weakly prime, because it can be changed into another prime (21665389) 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, 10832844 + 10832845.

It is an arithmetic number, because the mean of its divisors is an integer number (10832845).

Almost surely, 2^21665689 is an apocalyptic number.

It is an amenable number.

21665689 is a deficient number, since it is larger than the sum of its proper divisors (1).

21665689 is an equidigital number, since it uses as much as digits as its factorization.

21665689 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 155520, while the sum is 43.

The square root of 21665689 is about 4654.6416618253. The cubic root of 21665689 is about 278.7773603554. Note that the first 3 decimals are identical.

The spelling of 21665689 in words is "twenty-one million, six hundred sixty-five thousand, six hundred eighty-nine".