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 A226290 Irregular triangle read by rows: T(n,k) is the number of binary pattern classes in the (3,n)-rectangular grid with k '1's and (3n-k) '0's: two patterns are in same class if one of them can be obtained by a reflection or 180-degree rotation of the other. 35
 1, 1, 2, 2, 1, 1, 2, 6, 6, 6, 2, 1, 1, 4, 13, 27, 39, 39, 27, 13, 4, 1, 1, 4, 22, 60, 139, 208, 252, 208, 139, 60, 22, 4, 1, 1, 6, 34, 129, 371, 794, 1310, 1675, 1675, 1310, 794, 371, 129, 34, 6, 1, 1, 6, 48, 218, 813, 2196, 4767, 8070, 11139, 12300, 11139, 8070, 4767, 2196, 813, 218, 48, 6, 1 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,3 COMMENTS Sum of rows (see example) gives A225827. This triangle is to A225827 as Losanitsch's triangle A034851 is to A005418, and triangle A226048 to A225826. By columns: T(n,1) is A052928. T(n,2) is A226292. Also the number of equivalence classes of ways of placing k 1 X 1 tiles in an n X 3 rectangle under all symmetry operations of the rectangle. - Christopher Hunt Gribble, Apr 24 2015 LINKS Yosu Yurramendi, María Merino, Rows n = 0..30 of irregular triangle, flattened EXAMPLE n\k 0 1  2   3   4    5    6    7     8     9    10   11   12 0   1 1   1 2  2   1 2   1 2  6   6   6    2    1 3   1 4 13  27  39   39   27   13     4     1 4   1 4 22  60 139  208  252  208   139    60    22    4    1 5   1 6 34 129 371  794 1310 1675  1675  1310   794  371  129    34   6   1 6   1 6 48 218 813 2196 4767 8070 11139 12300 11139 8070 4767  2196 813 218 48 6 1 ... The length of row n is 3*n+1. MATHEMATICA T[n_, k_] := (Binomial[3n, k] + If[OddQ[n] || EvenQ[k], Binomial[Quotient[3 n, 2], Quotient[k, 2]], 0] + Sum[Binomial[n, k - 2i] Binomial[n, i] + Binomial[3 Mod[n, 2], k - 2i] Binomial[3 Quotient[n, 2], i], {i, 0, Quotient[k, 2]}])/4; Table[T[n, k], {n, 0, 6}, {k, 0, 3n}] // Flatten (* Jean-François Alcover, Oct 06 2017, after Andrew Howroyd *) PROG (PARI) T(n, k)={(binomial(3*n, k) + if(n%2==1||k%2==0, binomial(3*n\2, k\2), 0) + sum(i=0, k\2, binomial(n, k-2*i) * binomial(1*n, i) + binomial(3*(n%2), k-2*i) * binomial(3*(n\2), i)))/4} for(n=0, 6, for(k=0, 3*n, print1(T(n, k), ", ")); print) \\ Andrew Howroyd, May 30 2017 CROSSREFS Cf. A225826, A225827, A005418, A034851, A226048. Sequence in context: A322058 A244006 A110283 * A235342 A079692 A110269 Adjacent sequences:  A226287 A226288 A226289 * A226291 A226292 A226293 KEYWORD nonn,tabf AUTHOR Yosu Yurramendi, Jun 02 2013 EXTENSIONS Definition corrected by María Merino, May 19 2017 STATUS approved

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Last modified October 16 05:50 EDT 2019. Contains 328044 sequences. (Running on oeis4.)