21166011661 has 2 divisors, whose sum is σ = 21166011662. Its totient is φ = 21166011660.

The previous prime is 21166011641. The next prime is 21166011703. The reversal of 21166011661 is 16611066112.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 15141302500 + 6024709161 = 123050^2 + 77619^2 .

It is a cyclic number.

It is not a de Polignac number, because 21166011661 - 2⁹ = 21166011149 is a prime.

It is a super-3 number, since 3×21166011661³ (a number of 32 digits) contains 333 as substring.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21166011611) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10583005830 + 10583005831.

It is an arithmetic number, because the mean of its divisors is an integer number (10583005831).

Almost surely, 2^21166011661 is an apocalyptic number.

It is an amenable number.

21166011661 is a deficient number, since it is larger than the sum of its proper divisors (1).

21166011661 is an equidigital number, since it uses as much as digits as its factorization.

21166011661 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 2592, while the sum is 31.

Adding to 21166011661 its reverse (16611066112), we get a palindrome (37777077773).

The spelling of 21166011661 in words is "twenty-one billion, one hundred sixty-six million, eleven thousand, six hundred sixty-one".