21665386651 has 2 divisors, whose sum is σ = 21665386652. Its totient is φ = 21665386650.

The previous prime is 21665386627. The next prime is 21665386703. The reversal of 21665386651 is 15668356612.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 21665386651 - 2¹⁵ = 21665353883 is a prime.

It is a junction number, because it is equal to n+sod(n) for n = 21665386595 and 21665386604.

It is not a weakly prime, because it can be changed into another prime (21665386621) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10832693325 + 10832693326.

It is an arithmetic number, because the mean of its divisors is an integer number (10832693326).

Almost surely, 2^21665386651 is an apocalyptic number.

21665386651 is a deficient number, since it is larger than the sum of its proper divisors (1).

21665386651 is an equidigital number, since it uses as much as digits as its factorization.

21665386651 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 1555200, while the sum is 49.

The spelling of 21665386651 in words is "twenty-one billion, six hundred sixty-five million, three hundred eighty-six thousand, six hundred fifty-one".