2161636781 has 2 divisors, whose sum is σ = 2161636782. Its totient is φ = 2161636780.

The previous prime is 2161636739. The next prime is 2161636793. The reversal of 2161636781 is 1876361612.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 1827990025 + 333646756 = 42755^2 + 18266^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-2161636781 is a prime.

It is a super-2 number, since 2×2161636781² = 9345347145944083922, which contains 22 as substring.

It is an alternating number because its digits alternate between even and odd.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (2161636181) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 1080818390 + 1080818391.

It is an arithmetic number, because the mean of its divisors is an integer number (1080818391).

Almost surely, 2^2161636781 is an apocalyptic number.

It is an amenable number.

2161636781 is a deficient number, since it is larger than the sum of its proper divisors (1).

2161636781 is an equidigital number, since it uses as much as digits as its factorization.

2161636781 is an evil number, because the sum of its binary digits is even.

The product of its digits is 72576, while the sum is 41.

The square root of 2161636781 is about 46493.4057797447. The cubic root of 2161636781 is about 1292.9872443362.

The spelling of 2161636781 in words is "two billion, one hundred sixty-one million, six hundred thirty-six thousand, seven hundred eighty-one".