81965561 has 2 divisors, whose sum is σ = 81965562. Its totient is φ = 81965560.

The previous prime is 81965557. The next prime is 81965579. The reversal of 81965561 is 16556918.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 80209936 + 1755625 = 8956^2 + 1325^2 .

It is a cyclic number.

It is not a de Polignac number, because 81965561 - 2² = 81965557 is a prime.

It is a Chen prime.

It is not a weakly prime, because it can be changed into another prime (81925561) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 40982780 + 40982781.

It is an arithmetic number, because the mean of its divisors is an integer number (40982781).

Almost surely, 2^81965561 is an apocalyptic number.

It is an amenable number.

81965561 is a deficient number, since it is larger than the sum of its proper divisors (1).

81965561 is an equidigital number, since it uses as much as digits as its factorization.

81965561 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 64800, while the sum is 41.

The square root of 81965561 is about 9053.4833627726. The cubic root of 81965561 is about 434.3873190854.

The spelling of 81965561 in words is "eighty-one million, nine hundred sixty-five thousand, five hundred sixty-one".