21666853391 has 2 divisors, whose sum is σ = 21666853392. Its totient is φ = 21666853390.

The previous prime is 21666853363. The next prime is 21666853423. The reversal of 21666853391 is 19335866612.

It is a happy number.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 21666853391 - 2¹⁰ = 21666852367 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21666853301) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10833426695 + 10833426696.

It is an arithmetic number, because the mean of its divisors is an integer number (10833426696).

Almost surely, 2^21666853391 is an apocalyptic number.

21666853391 is a deficient number, since it is larger than the sum of its proper divisors (1).

21666853391 is an equidigital number, since it uses as much as digits as its factorization.

21666853391 is an evil number, because the sum of its binary digits is even.

The product of its digits is 1399680, while the sum is 50.

The spelling of 21666853391 in words is "twenty-one billion, six hundred sixty-six million, eight hundred fifty-three thousand, three hundred ninety-one".