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 A080381 Triangle read by rows: GCD[C[n,Floor[n/2]],C[n,i], i=0,...n; greatest common divisor of binomial coefficients and corresponding central binomial coefficient. 5
 1, 1, 1, 1, 2, 1, 1, 3, 3, 1, 1, 2, 6, 2, 1, 1, 5, 10, 10, 5, 1, 1, 2, 5, 20, 5, 2, 1, 1, 7, 7, 35, 35, 7, 7, 1, 1, 2, 14, 14, 70, 14, 14, 2, 1, 1, 9, 18, 42, 126, 126, 42, 18, 9, 1, 1, 2, 9, 12, 42, 252, 42, 12, 9, 2, 1, 1, 11, 11, 33, 66, 462, 462, 66, 33, 11, 11, 1, 1, 12, 66, 44, 33, 132 (list; table; graph; refs; listen; history; text; internal format)
 OFFSET 0,5 COMMENTS The matrix inverse starts 1; -1,1; 1,-2,1; -1,3,-3,1; -3,4,0,-2,1; 19,-35,20,0,-5,1; -7,-2,15,-10,5,-2,1; 55,21,-147,105,-35,7,-7,1 -67,180,-168,56,0,0,0,-2,1; - R. J. Mathar, Mar 21 2013 LINKS EXAMPLE Triangle begins: 1 1 1 1 2 1 1 3 3 1 1 2 6 2 1 1 5 10 10 5 1 1 2 5 20 5 2 1 1 7 7 35 35 7 7 1 MAPLE A080381 := proc(n, k)     if k < 0 or k > n then         0;     else         igcd(binomial(n, floor(n/2)), binomial(n, k)) ;     end if; end proc: # R. J. Mathar, Mar 21 2013 MATHEMATICA Table[Table[GCD[Binomial[n, j], Binomial[n, Floor[n/2]]], {j, 0, n}], {n, 1, 10}] CROSSREFS Cf. A007318, A001405. Sequence in context: A132422 A065133 A204087 * A080396 A155582 A169946 Adjacent sequences:  A080378 A080379 A080380 * A080382 A080383 A080384 KEYWORD nonn,tabl AUTHOR Labos E. (labos(AT)ana.sote.hu), Mar 12 2003 STATUS approved

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