81561089 has 2 divisors, whose sum is σ = 81561090. Its totient is φ = 81561088.

The previous prime is 81561049. The next prime is 81561107. The reversal of 81561089 is 98016518.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 70224400 + 11336689 = 8380^2 + 3367^2 .

It is a cyclic number.

It is not a de Polignac number, because 81561089 - 2¹⁶ = 81495553 is a prime.

It is a super-2 number, since 2×81561089² = 13304422477731842, which contains 22 as substring.

It is not a weakly prime, because it can be changed into another prime (81561049) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 40780544 + 40780545.

It is an arithmetic number, because the mean of its divisors is an integer number (40780545).

Almost surely, 2^81561089 is an apocalyptic number.

It is an amenable number.

81561089 is a deficient number, since it is larger than the sum of its proper divisors (1).

81561089 is an equidigital number, since it uses as much as digits as its factorization.

81561089 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 17280, while the sum is 38.

The square root of 81561089 is about 9031.1178156416. The cubic root of 81561089 is about 433.6716229530.

The spelling of 81561089 in words is "eighty-one million, five hundred sixty-one thousand, eighty-nine".