811561 has 2 divisors, whose sum is σ = 811562. Its totient is φ = 811560.

The previous prime is 811553. The next prime is 811583. The reversal of 811561 is 165118.

It is an a-pointer prime, because the next prime (811583) can be obtained adding 811561 to its sum of digits (22).

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 712336 + 99225 = 844^2 + 315^2 .

It is a cyclic number.

It is not a de Polignac number, because 811561 - 2³ = 811553 is a prime.

It is not a weakly prime, because it can be changed into another prime (811501) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 405780 + 405781.

It is an arithmetic number, because the mean of its divisors is an integer number (405781).

2⁸¹¹⁵⁶¹ is an apocalyptic number.

It is an amenable number.

811561 is a deficient number, since it is larger than the sum of its proper divisors (1).

811561 is an equidigital number, since it uses as much as digits as its factorization.

811561 is an evil number, because the sum of its binary digits is even.

The product of its digits is 240, while the sum is 22.

The square root of 811561 is about 900.8668048052. The cubic root of 811561 is about 93.2768181101.

Adding to 811561 its product of digits (240), we get a square (811801 = 901²).

Adding to 811561 its reverse (165118), we get a palindrome (976679).

The spelling of 811561 in words is "eight hundred eleven thousand, five hundred sixty-one".