2105661781 has 2 divisors, whose sum is σ = 2105661782. Its totient is φ = 2105661780.

The previous prime is 2105661739. The next prime is 2105661821. The reversal of 2105661781 is 1871665012.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 2100755556 + 4906225 = 45834^2 + 2215^2 .

It is a cyclic number.

It is not a de Polignac number, because 2105661781 - 2¹⁹ = 2105137493 is a prime.

It is a super-2 number, since 2×2105661781² = 8867623071928183922, which contains 22 as substring.

It is a self number, because there is not a number n which added to its sum of digits gives 2105661781.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (2105661721) 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, 1052830890 + 1052830891.

It is an arithmetic number, because the mean of its divisors is an integer number (1052830891).

Almost surely, 2^2105661781 is an apocalyptic number.

It is an amenable number.

2105661781 is a deficient number, since it is larger than the sum of its proper divisors (1).

2105661781 is an equidigital number, since it uses as much as digits as its factorization.

2105661781 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 20160, while the sum is 37.

The square root of 2105661781 is about 45887.4904630881. The cubic root of 2105661781 is about 1281.7289828706.

The spelling of 2105661781 in words is "two billion, one hundred five million, six hundred sixty-one thousand, seven hundred eighty-one".