1811561 has 2 divisors, whose sum is σ = 1811562. Its totient is φ = 1811560.

The previous prime is 1811539. The next prime is 1811567. The reversal of 1811561 is 1651181.

It is a happy number.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 1771561 + 40000 = 1331^2 + 200^2 .

It is a cyclic number.

It is not a de Polignac number, because 1811561 - 2¹⁸ = 1549417 is a prime.

It is not a weakly prime, because it can be changed into another prime (1811567) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 905780 + 905781.

It is an arithmetic number, because the mean of its divisors is an integer number (905781).

2^1811561 is an apocalyptic number.

It is an amenable number.

1811561 is a deficient number, since it is larger than the sum of its proper divisors (1).

1811561 is an equidigital number, since it uses as much as digits as its factorization.

1811561 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 240, while the sum is 23.

The square root of 1811561 is about 1345.9424207595. The cubic root of 1811561 is about 121.9039152081.

The spelling of 1811561 in words is "one million, eight hundred eleven thousand, five hundred sixty-one".