2181291661 has 2 divisors, whose sum is σ = 2181291662. Its totient is φ = 2181291660.

The previous prime is 2181291653. The next prime is 2181291683. The reversal of 2181291661 is 1661921812.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 1997553636 + 183738025 = 44694^2 + 13555^2 .

It is a cyclic number.

It is not a de Polignac number, because 2181291661 - 2³ = 2181291653 is a prime.

It is a self number, because there is not a number n which added to its sum of digits gives 2181291661.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (2181291601) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 1090645830 + 1090645831.

It is an arithmetic number, because the mean of its divisors is an integer number (1090645831).

Almost surely, 2^2181291661 is an apocalyptic number.

It is an amenable number.

2181291661 is a deficient number, since it is larger than the sum of its proper divisors (1).

2181291661 is an equidigital number, since it uses as much as digits as its factorization.

2181291661 is an evil number, because the sum of its binary digits is even.

The product of its digits is 10368, while the sum is 37.

The square root of 2181291661 is about 46704.3002409842. The cubic root of 2181291661 is about 1296.8942946496.

The spelling of 2181291661 in words is "two billion, one hundred eighty-one million, two hundred ninety-one thousand, six hundred sixty-one".