21665389 has 2 divisors, whose sum is σ = 21665390. Its totient is φ = 21665388.

The previous prime is 21665383. The next prime is 21665401. The reversal of 21665389 is 98356612.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 18992164 + 2673225 = 4358^2 + 1635^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21665389 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21665383) 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, 10832694 + 10832695.

It is an arithmetic number, because the mean of its divisors is an integer number (10832695).

Almost surely, 2^21665389 is an apocalyptic number.

It is an amenable number.

21665389 is a deficient number, since it is larger than the sum of its proper divisors (1).

21665389 is an equidigital number, since it uses as much as digits as its factorization.

21665389 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 77760, while the sum is 40.

The square root of 21665389 is about 4654.6094358174. The cubic root of 21665389 is about 278.7760736267.

The spelling of 21665389 in words is "twenty-one million, six hundred sixty-five thousand, three hundred eighty-nine".