# [seqfan] Re: Knight Tour recurrences - same as King Tour

Ron Hardin rhhardin at att.net
Sat Feb 26 02:17:29 CET 2011

```Quick computation of all the 3-move tours for various pieces in the job queue
gives (with a surprise)

16 104 328 664 1112 1672 2344 3128 4024 5032 6152 7384 8728 10184 11752 13432
15224 17128 19144 21272 23512 25864 28328 30904 33592 36392
Number of 3-step knight's tours on a (n+2)X(n+2) board summed over all starting
positions
Empirical: a(n)=3*a(n-1)-3*a(n-2)+a(n-3) for n>4

0 24 160 408 768 1240 1824 2520 3328 4248 5280 6424 7680 9048 10528 12120 13824
15640 17568 19608 21760 24024 26400 28888 31488 34200 37024 39960
Number of 3-step king's tours on a nXn board summed over all starting positions
Empirical: a(n)=3*a(n-1)-3*a(n-2)+a(n-3)

0 8 44 104 188 296 428 584 764 968 1196 1448 1724 2024 2348
Number of 3-step one space at a time rook's tours on a nXn board summed over all
starting positions
Empirical: a(n)=3*a(n-1)-3*a(n-2)+a(n-3) for n>4

0 8 108 480 1400 3240 6468 11648 19440 30600 45980 66528 93288 127400 170100
222720 286688
Number of 3-turn rook's tours on a nXn board summed over all starting positions
Empirical: a(n)=5*a(n-1)-10*a(n-2)+10*a(n-3)-5*a(n-4)+a(n-5)

0 24 296 1304 3808 8832 17672 31888 53312 84040 126440 183144 257056 351344
469448
Number of 3-turn queen's tours on a nXn board summed over all starting positions
Empirical: a(n)=4*a(n-1)-5*a(n-2)+5*a(n-4)-4*a(n-5)+a(n-6)

0 0 28 152 488 1192 2468 4560 7760 12400 18860 27560 38968 53592 71988
Number of 3-turn bishop's tours on a nXn board summed over all starting
positions
Empirical: a(n)=4*a(n-1)-5*a(n-2)+5*a(n-4)-4*a(n-5)+a(n-6)

0 0 20 64 132 224 340 480 644 832 1044 1280 1540 1824 2132
Number of 3-step one space at a time bishop's tours on a nXn board summed over
all starting positions
Empirical: a(n)=3*a(n-1)-3*a(n-2)+a(n-3) for n>4

The 1 4 5 0 5 4 1 pair is a surprise.  So much for my polynomial conjecture.

rhhardin at mindspring.com
rhhardin at att.net (either)

----- Original Message ----
> From: "franktaw at netscape.net" <franktaw at netscape.net>
> To: seqfan at list.seqfan.eu
> Sent: Fri, February 25, 2011 5:19:37 PM
> Subject: [seqfan] Re: Knight Tour recurrences - same as King Tour
>
> Probably you will only see that recurrence for pieces with only a finite
>(bounded) number of moves on any turn. I'm going to go out on a limb and guess
>that you will see a recurrence 4a(n-1) - 6a(n-2) + 4a(n-3) - a(n-4) for pieces
>with unbounded moves.
>
>
> -----Original  Message-----
> From: Ron Hardin <rhhardin at att.net>
>
> Knight tour  counts have the same recurrence as the king tour counts (row 1 of
> course is  automatic, but for all rows to have the same recurrence still
seems
> surprising), suggesting now a wild guess that any sort of piece-move  will
have
> that same recurrence; I don't have enough numbers yet to  tell.
>
> T(n,k)=Number of n-step knight's tours on a (k+2)X(k+2) board  summed over all
> starting positions
>
> Table  starts
> ..9...16.....25......36......49......64......81.....100....121....144...1
> 69
> .16...48.....96.....160.....240.....336.....448.....576....720....880..10
> 56
> .16..104....328.....664....1112....1672....2344....3128...4024...5032..61
> 52
> .16..208....976....2576....5056....8320...12368...17200..22816..29216.364
> 00
> .16..400...2800....9328...21480...39616...63440...92656.127264.167264....
> ..
> .16..800...8352...34448...91328..186544..322528..498320.712080...........
> ..
> .16.1280..21664..118480..372384..847520.1584576.2596480..................
> ..
> .16.2208..57392..405040.1508784.3846192.7777808..........................
> ..
> ..0.3184.135184.1290112.5807488..........................................
> ..
> ..0.4640.317296.4089632..................................................
> ..
>
> Empirical,  for all rows: a(n)=3*a(n-1)-3*a(n-2)+a(n-3) for  n>3,3,4,6,8,10
> respectively for row in 1..6
> rhhardin at mindspring.com
> rhhardin at att.net (either)
>
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>
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>

```