81661189 has 2 divisors, whose sum is σ = 81661190. Its totient is φ = 81661188.

The previous prime is 81661159. The next prime is 81661199. The reversal of 81661189 is 98116618.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 64272289 + 17388900 = 8017^2 + 4170^2 .

It is a cyclic number.

It is not a de Polignac number, because 81661189 - 2⁷ = 81661061 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (81661159) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 40830594 + 40830595.

It is an arithmetic number, because the mean of its divisors is an integer number (40830595).

Almost surely, 2^81661189 is an apocalyptic number.

It is an amenable number.

81661189 is a deficient number, since it is larger than the sum of its proper divisors (1).

81661189 is an equidigital number, since it uses as much as digits as its factorization.

81661189 is an evil number, because the sum of its binary digits is even.

The product of its digits is 20736, while the sum is 40.

The square root of 81661189 is about 9036.6580659002. The cubic root of 81661189 is about 433.8489656166.

The spelling of 81661189 in words is "eighty-one million, six hundred sixty-one thousand, one hundred eighty-nine".