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A077539
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a(n) = Floor[ T(n+1)!*T(n-1)!/{(T(n)!)^2}, where T(n) = n(n+1)/2 = the n-th triangular number.
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0
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6, 20, 42, 71, 108, 152, 204, 263, 330, 403, 485, 573, 669, 773, 884, 1002, 1128, 1261, 1401, 1549, 1704, 1866, 2036, 2214, 2398, 2591, 2790, 2997, 3211, 3433, 3662, 3898, 4142, 4394, 4652, 4918, 5192, 5472, 5761, 6056, 6359, 6669, 6987
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,1
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COMMENTS
| The ratio itself is an integer only for n = 1, 2 and 3.
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EXAMPLE
| a(1) = 6 = (2*3)/1, a(2) = 20 = (4*5*6)/(2*3) etc.
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CROSSREFS
| Sequence in context: A031052 A097811 A143711 * A002943 A068377 A009946
Adjacent sequences: A077536 A077537 A077538 * A077540 A077541 A077542
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KEYWORD
| nonn
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AUTHOR
| Amarnath Murthy (amarnath_murthy(AT)yahoo.com), Nov 09 2002
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EXTENSIONS
| More terms from Mark Hudson (mrmarkhudson(AT)hotmail.com), Feb 11 2003
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