Onitiu Problem 30x30 Solution

 This was the most difficult to solve so far. It shows a knight tour with 90 degree rotational symmetry with the square numbers in a closed knight path (the red line). There are sixteen cells (marked by squares) where the four circuits intersect. The initial and final cells of each circuit are marked by a darker square (001 and 900 in the case of the circuit of square numbers). 

Solution to Onitiu Problem 30x30

The thick black lines mark single-move links between the circuits. The dotted cells mark the links of two or three moves. These short links place considerable restrictions on the way the paths can be arranged.

Numerologists may notice that the numbers 666 and 216 (6 cubed) occupy diametrically opposite cells. This is because their difference is 450, half of 900.  

Locked Out of Twitter Again

 Twitter is again asking for a mobile phone number from me to sign in, but there doesn't seem to be any allowance for people who don't have mobile phones. I hope this is not becoming a general thing. It will mean that people without mobile phones are becoming second class citizens. I was also made to pass an "I'm Not A Robot" test, but apparently that was not sufficient! 

 

Another Onitiu Solution

After a couple of months I have at last solved another of the knight tours with 90 degree rotational symmetry and with the square numbers in a knight circuit (the red line). The type face for the numbers is necessarily vey small. They range from 001 to 676 which is the board size 26x26.

Onitiu 26x26 Birotary Solution