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 A175840 Mirror image of Nicomachus' table: T(n,k) = 3^(n-k)*2^k for n>=0 and 0<=k<=n. 4
 1, 3, 2, 9, 6, 4, 27, 18, 12, 8, 81, 54, 36, 24, 16, 243, 162, 108, 72, 48, 32, 729, 486, 324, 216, 144, 96, 64, 2187, 1458, 972, 648, 432, 288, 192, 128, 6561, 4374, 2916, 1944, 1296, 864, 576, 384, 256, 19683, 13122, 8748, 5832, 3888, 2592, 1728, 1152, 768, 512 (list; table; graph; refs; listen; history; text; internal format)
 OFFSET 0,2 COMMENTS Lenstra calls these numbers the harmonic numbers of Philippe de Vitry (1291-1361). De Vitry wanted to find pairs of harmonic numbers that differ by one. Levi ben Gerson, also known as Gersonides, proved in 1342 that there are only four pairs with this property of the form 2^n*3^m. See also Peterson’s story ‘Medieval Harmony’. This triangle is the mirror image of Nicomachus' table A036561. The triangle sums, see the crossrefs, mirror those of A036561. See A180662 for the definitions of these sums. LINKS Reinhard Zumkeller, Rows n = 0..120 of triangle, flattened J. O'Connor and E.F. Robertson, Nicomachus of Gerasa, The MacTutor History of Mathematics archive, 2010. Jay Kappraff, The Arithmetic of Nicomachus of Gerasa and its Applications to Systems of Proportion, Nexus Network Journal, vol. 2, no. 4 (October 2000). Hendrik Lenstra, Aeternitatem Cogita, Nieuw Archief voor Wiskunde, 5/2, maart 2001, pp. 23-28. Ivars Peterson, Medieval Harmony, Math Trek, Mathematical Association of America, 1998. FORMULA T(n,k) = 3^(n-k)*2^k for n>=0 and 0<=k<=n. T(n,n-k) = T(n,n-k+1) + T(n-1,n-k) for n>=1 and 1<=k<=n with T(n,n) = 2^n for n>=0. EXAMPLE 1; 3, 2; 9, 6, 4; 27, 18, 12, 8; 81, 54, 36, 24, 16; 243, 162, 108, 72, 48, 32; MAPLE A175840 := proc(n, k): 3^(n-k)*2^k end: seq(seq(A175840(n, k), k=0..n), n=0..9); MATHEMATICA Flatten[Table[3^(n-k) 2^k, {n, 0, 10}, {k, 0, n}]] (* Harvey P. Dale, May 08 2013 *) PROG (Haskell) a175840 n k = a175840_tabf !! n !! k a175840_row n = a175840_tabf !! n a175840_tabf = iterate (\xs@(x:_) -> x * 3 : map (* 2) xs)  -- Reinhard Zumkeller, Jun 08 2013 CROSSREFS Triangle sums: A001047 (Row1), A015441 (Row2), A016133 (Kn1 & Kn4), A005061 (Kn2 & Kn3), A016153 (Fi1& Fi2), A180844 (Ca1 & Ca4), A016140 (Ca2, Ca3), A180846 (Gi1 & Gi4), A180845 (Gi2 & Gi3), A016185 (Ze1 & Ze4), A180847 (Ze2 & Ze3). Cf. A000079, A000244, A000400, A003586. Sequence in context: A191539 A235539 A191449 * A125152 A229119 A269867 Adjacent sequences:  A175837 A175838 A175839 * A175841 A175842 A175843 KEYWORD easy,nonn,tabl AUTHOR Johannes W. Meijer, Sep 21 2010, Jul 13 2011, Jun 03 2012 STATUS approved

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Last modified December 1 13:22 EST 2021. Contains 349429 sequences. (Running on oeis4.)