21186791081 has 2 divisors, whose sum is σ = 21186791082. Its totient is φ = 21186791080.

The previous prime is 21186791077. The next prime is 21186791089. The reversal of 21186791081 is 18019768112.

It is a happy number.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 19913443225 + 1273347856 = 141115^2 + 35684^2 .

It is a cyclic number.

It is not a de Polignac number, because 21186791081 - 2² = 21186791077 is a prime.

It is a super-2 number, since 2×21186791081² (a number of 21 digits) contains 22 as substring.

It is not a weakly prime, because it can be changed into another prime (21186791089) 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, 10593395540 + 10593395541.

It is an arithmetic number, because the mean of its divisors is an integer number (10593395541).

Almost surely, 2^21186791081 is an apocalyptic number.

It is an amenable number.

21186791081 is a deficient number, since it is larger than the sum of its proper divisors (1).

21186791081 is an equidigital number, since it uses as much as digits as its factorization.

21186791081 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 48384, while the sum is 44.

The spelling of 21186791081 in words is "twenty-one billion, one hundred eighty-six million, seven hundred ninety-one thousand, eighty-one".