2165945981 has 2 divisors, whose sum is σ = 2165945982. Its totient is φ = 2165945980.

The previous prime is 2165945959. The next prime is 2165946007. The reversal of 2165945981 is 1895495612.

2165945981 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 1359101956 + 806844025 = 36866^2 + 28405^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-2165945981 is a prime.

It is a super-2 number, since 2×2165945981² = 9382643985220104722, which contains 22 as substring.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (2165945941) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 1082972990 + 1082972991.

It is an arithmetic number, because the mean of its divisors is an integer number (1082972991).

Almost surely, 2^2165945981 is an apocalyptic number.

It is an amenable number.

2165945981 is a deficient number, since it is larger than the sum of its proper divisors (1).

2165945981 is an equidigital number, since it uses as much as digits as its factorization.

2165945981 is an evil number, because the sum of its binary digits is even.

The product of its digits is 777600, while the sum is 50.

The square root of 2165945981 is about 46539.7247628303. The cubic root of 2165945981 is about 1293.8458594954.

The spelling of 2165945981 in words is "two billion, one hundred sixty-five million, nine hundred forty-five thousand, nine hundred eighty-one".