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 A167557 The lower left triangle of the ED1 array A167546. 5
 1, 1, 4, 2, 12, 32, 6, 48, 160, 384, 24, 240, 960, 2688, 6144, 120, 1440, 6720, 21504, 55296, 122880, 720, 10080, 53760, 193536, 552960, 1351680, 2949120, 5040, 80640, 483840, 1935360, 6082560, 16220160, 38338560, 82575360 (list; table; graph; refs; listen; history; text; internal format)
 OFFSET 1,3 COMMENTS We discovered that the numbers that appear in the lower left triangle of the ED1 array A167546 (m <= n) behave in a regular way, see the formula below. This rather simple regularity doesn't show up in the upper right triangle of the ED1 array (m > n). LINKS G. C. Greubel, Table of n, a(n) for the first 50 rows FORMULA a(n,m) = 4^(m-1)*(m-1)!*(n+m-2)!/(2*m-2)!. EXAMPLE The first few triangle rows are: [1] [1, 4] [2, 12, 32] [6, 48, 160, 384] [24, 240, 960, 2688, 6144] [120, 1440, 6720, 21504, 55296, 122880] MAPLE a := proc(n, m): 4^(m-1)*(m-1)!*(n+m-2)!/(2*m-2)! end: seq(seq(a(n, m), m=1..n), n=1..8);  # Johannes W. Meijer, revised Nov 23 2012 MATHEMATICA Flatten[Table[(4^(m-1) (m-1)!(n+m-2)!)/(2m-2)!, {n, 10}, {m, n}]] (* Harvey P. Dale, Sep 29 2013 *) CROSSREFS A167546 is the ED1 array. A047053 and A167558 are the first two right hand triangle columns. A000142, 4*A001710 (n>=2), 32*A001720, 384*A001730, 6144*A049389, 122880*A051431 are the first six left hand triangle columns. A167559 equals the row sums. Sequence in context: A154345 A058095 A105196 * A069836 A224820 A125153 Adjacent sequences:  A167554 A167555 A167556 * A167558 A167559 A167560 KEYWORD easy,nonn,tabl AUTHOR Johannes W. Meijer, Nov 10 2009 STATUS approved

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Last modified February 22 18:24 EST 2020. Contains 332148 sequences. (Running on oeis4.)