21666739538669 has 2 divisors, whose sum is σ = 21666739538670. Its totient is φ = 21666739538668.

The previous prime is 21666739538651. The next prime is 21666739538671. The reversal of 21666739538669 is 96683593766612.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 21593819017225 + 72920521444 = 4646915^2 + 270038^2 .

It is a cyclic number.

It is not a de Polignac number, because 21666739538669 - 2³² = 21662444571373 is a prime.

It is a super-2 number, since 2×21666739538669² (a number of 27 digits) contains 22 as substring.

Together with 21666739538671, it forms a pair of twin primes.

It is a Chen prime.

It is a self number, because there is not a number n which added to its sum of digits gives 21666739538669.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21666739531669) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (23) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10833369769334 + 10833369769335.

It is an arithmetic number, because the mean of its divisors is an integer number (10833369769335).

Almost surely, 2^{21666739538669} is an apocalyptic number.

It is an amenable number.

21666739538669 is a deficient number, since it is larger than the sum of its proper divisors (1).

21666739538669 is an equidigital number, since it uses as much as digits as its factorization.

21666739538669 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 3174474240, while the sum is 77.

The spelling of 21666739538669 in words is "twenty-one trillion, six hundred sixty-six billion, seven hundred thirty-nine million, five hundred thirty-eight thousand, six hundred sixty-nine".