A269526 Square array T(n,k) (n>=1, k>=1) read by antidiagonals upwards in which each term is the least positive integer satisfying the condition that no row, column, diagonal, or antidiagonal contains a repeated term.
1, 2, 3, 3, 4, 2, 4, 1, 5, 6, 5, 2, 6, 1, 4, 6, 7, 3, 2, 8, 5, 7, 8, 1, 5, 9, 3, 10, 8, 5, 9, 4, 1, 7, 6, 11, 9, 6, 4, 7, 2, 8, 5, 12, 13, 10, 11, 7, 3, 5, 6, 9, 4, 14, 8, 11, 12, 8, 9, 6, 10, 3, 7, 15, 16, 14, 12, 9, 13, 10, 11, 14, 4, 15, 16, 17, 7, 18, 13, 10, 14, 11, 3, 4, 8, 16, 9, 6, 12, 15, 7
Offset: 1
Examples
The array is constructed along its antidiagonals, in the following way: a(1) a(3) a(6) a(10) a(2) a(5) a(9) a(4) a(8) a(7) See the link from Peter Kagey for an animated example. The beginning of the square array is: 1, 3, 2, 6, 4, 5, 10, 11, 13, 8, 14, 18, 7, 20, 19, 9, 12, ... 2, 4, 5, 1, 8, 3, 6, 12, 14, 16, 7, 15, 17, 9, 22, 21, 11, ... 3, 1, 6, 2, 9, 7, 5, 4, 15, 17, 12, 19, 18, 21, 8, 10, 23, ... 4, 2, 3, 5, 1, 8, 9, 7, 16, 6, 18, 17, 11, 10, 23, 22, 14, ... 5, 7, 1, 4, 2, 6, 3, 15, 9, 10, 13, 8, 20, 14, 12, 11, 17, ... 6, 8, 9, 7, 5, 10, 4, 16, 2, 1, 3, 11, 22, 15, 24, 13, 27, ... 7, 5, 4, 3, 6, 14, 8, 9, 11, 18, 2, 21, 1, 16, 10, 12, 20, ... 8, 6, 7, 9, 11, 4, 13, 3, 12, 15, 1, 10, 2, 5, 26, 14, 18, ... 9, 11, 8, 10, 3, 1, 14, 6, 7, 13, 4, 12, 24, 18, 2, 5, 19, ... 10, 12, 13, 11, 16, 2, 17, 5, 20, 9, 8, 14, 4, 6, 1, 7, 3, ... 11, 9, 14, 12, 10, 15, 1, 8, 21, 7, 16, 20, 5, 3, 18, 17, 32, ... 12, 10, 11, 8, 7, 9, 2, 13, 5, 23, 25, 26, 14, 17, 16, 15, 33, ... ... - _N. J. A. Sloane_, Jun 29 2016
Links
- Peter Kagey, Table of n, a(n) for n = 1..10000
- F. Michel Dekking, Jeffrey Shallit, and N. J. A. Sloane, Queens in exile: non-attacking queens on infinite chess boards, Electronic J. Combin., 27:1 (2020), #P1.52.
- Peter Kagey, Animated example illustrating the first fifteen terms.
Crossrefs
Main diagonal is A274318.
Column 1 is A000027, column 2 is A256008(n) = A004443(n-1)+1 = 1 + (nimsum of n-1 and 2), column 3 is A274614 (or equally, A274615 + 1), and column 4 is A274617 (or equally, A274619 + 1).
If all terms are reduced by 1 and the offset is changed to 0 we get A274528.
See A274630 for the case where both queens' and knights' moves must avoid duplicates.
Programs
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Haskell
import Data.List ((\\)) a269526 n = head $ [1..] \\ map a269526 (a274080_row n) -- Peter Kagey, Jun 10 2016
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Maple
# The following Maple program was provided at my request by Alois P. Heinz, who said that he had not posted it himself because it stores the data in an inefficient way. - N. J. A. Sloane, Jul 01 2016 A:= proc(n, k) option remember; local m, s; if n=1 and k=1 then 1 else s:= {seq(A(i,k), i=1..n-1), seq(A(n,j), j=1..k-1), seq(A(n-t,k-t), t=1..min(n,k)-1), seq(A(n+j,k-j), j=1..k-1)}; for m while m in s do od; m fi end: [seq(seq(A(1+d-k, k), k=1..d), d=1..15)];
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Mathematica
A[n_, k_] := A[n, k] = If[n == 1 && k == 1, 1, s = {Table[A[i, k], {i, 1, n-1}], Table[A[n, j], {j, 1, k-1}], Table[A[n-t, k-t], {t, 1, Min[n, k] - 1}], Table[A[n+j, k-j], {j, 1, k-1}]} // Flatten; For[m = 1, True, m++, If[FreeQ[s, m], Return[m]]]]; Table[Table[A[1+d-k, k], {k, 1, d}], {d, 1, 15}] // Flatten (* Jean-François Alcover, Jul 21 2016, translated from Maple *) -
PARI
{M269526=Map(); A269526=T(r,c)=c>1 && !mapisdefined(M269526, [r,c], &r) && mapput(M269526, [r,c], r=sum(k=1, #c=Set(concat([[T(r+k,c+k)|k<-[1-min(r, c)..-1]], [T(r,k)|k<-[1..c-1]], [T(k,c)|k<-[1..r-1]], [T(r+c-k,k)|k<-[1..c-1]]])), c[k]==k)+1); r} \\ M. F. Hasler, Sep 26 2022
Formula
Theorem 1: T(n,1) = n.
Proof by induction. T(1,1)=1 by definition. When calculating T(n,1), the only constraint is that it be different from all earlier entries in the first column, which are 1,2,3,...,n-1. So T(n,1)=n. QED
Theorem 2 (Based on a message from Bob Selcoe, Jun 29 2016): Write n = 4t+i with t >= 0, i=1,2,3, or 4. Then T(n,2) = 4t+3 if i=1, 4t+4 if i=2, 4t+1 if i=3, 4t+2 if i=4. This implies that the second column is the permutation A256008.
Proof: We check that the first 4 entries in column 2 are 2,5,6,3. From then on, to calculate the entry T(n,2), we need only look to the N, NW, W, and SW (we need never look to the East). After we have found the first 4t entries in the column, the column contains all the numbers from 1 to 4t. The four smallest free numbers are 4t+1, 4t+2, 4t+3, 4t+4. Entry T(4t+1,2) cannot be 4t+1 or 4t+2, but it can (and therefore must) be 4t+3. Similarly T(4t+2,2)=4t+4, T(4t+3,2)=4t+1, and T(4t+4,2)=4t+2. The column now contains all the numbers from 1 to 4t+4. Repeating this argument established the theorem. QED
Comments from Bob Selcoe, Jun 29 2016: (Start)
From Theorem 2, column 2 (i.e., terms a((j^2+j+4)/2), j>=1) is a permutation. After a(3)=3, the differences of successive terms follow the pattern a(n) = 3 [+1, -3, +1, +5], so a(5)=4, a(8)=1, a(12)=2, a(17)=7, a(23)=8, a(30)=5...
Similarly, column 3 (i.e., terms a((j^2+j+6)/2), j>=2) appears to be a permutation, but with the pattern after a(6)=2 and a(9)=5 being 5 [+1, -3, -2, +8, -5, +3, +1, +5, +1, -3, +1, -2, +8, -3, +1, +5]. (See A274614 and A274615.)
I conjecture that other similar cyclical difference patterns should hold for any column k (i.e., terms a((j^2+j+2*k)/2), j>=k-1), so that each column is a permutation.
Also, the differences in column 1 are a 1-cycle ([+1]), in column 2 a 4-cycle after the first term, and in column 3 a 16-cycle after the second term. Perhaps the cycle lengths are 4^(k-1) starting after j=k-1. (End) WARNING: These comments may be wrong - see COMMENTS section. - N. J. A. Sloane, Sep 26 2022
Extensions
Definition clarified by Omar E. Pol, Jun 29 2016
Comments