2164521607681 has 2 divisors, whose sum is σ = 2164521607682. Its totient is φ = 2164521607680.

The previous prime is 2164521607679. The next prime is 2164521607693. The reversal of 2164521607681 is 1867061254612.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 1185084795456 + 979436812225 = 1088616^2 + 989665^2 .

It is a cyclic number.

It is not a de Polignac number, because 2164521607681 - 2¹ = 2164521607679 is a prime.

It is a super-2 number, since 2×2164521607681² (a number of 25 digits) contains 22 as substring.

Together with 2164521607679, it forms a pair of twin primes.

It is not a weakly prime, because it can be changed into another prime (2164521607981) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 1082260803840 + 1082260803841.

It is an arithmetic number, because the mean of its divisors is an integer number (1082260803841).

Almost surely, 2^{2164521607681} is an apocalyptic number.

It is an amenable number.

2164521607681 is a deficient number, since it is larger than the sum of its proper divisors (1).

2164521607681 is an equidigital number, since it uses as much as digits as its factorization.

2164521607681 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 967680, while the sum is 49.

The spelling of 2164521607681 in words is "two trillion, one hundred sixty-four billion, five hundred twenty-one million, six hundred seven thousand, six hundred eighty-one".