21661699809857 has 2 divisors, whose sum is σ = 21661699809858. Its totient is φ = 21661699809856.

The previous prime is 21661699809839. The next prime is 21661699809917. The reversal of 21661699809857 is 75890899616612.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 20734945102096 + 926754707761 = 4553564^2 + 962681^2 .

It is a cyclic number.

It is not a de Polignac number, because 21661699809857 - 2⁶ = 21661699809793 is a prime.

It is not a weakly prime, because it can be changed into another prime (21661609809857) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (19) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10830849904928 + 10830849904929.

It is an arithmetic number, because the mean of its divisors is an integer number (10830849904929).

Almost surely, 2^{21661699809857} is an apocalyptic number.

It is an amenable number.

21661699809857 is a deficient number, since it is larger than the sum of its proper divisors (1).

21661699809857 is an equidigital number, since it uses as much as digits as its factorization.

21661699809857 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 705438720, while the sum is 77.

The spelling of 21661699809857 in words is "twenty-one trillion, six hundred sixty-one billion, six hundred ninety-nine million, eight hundred nine thousand, eight hundred fifty-seven".