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A077539 a(n) = floor(T(n+1)!*T(n-1)!/(T(n)!)^2), where T(n) = n(n+1)/2 = the n-th triangular number. 0
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; text; internal format)
OFFSET
1,1
COMMENTS
The ratio itself is an integer only for n = 1, 2 and 3.
LINKS
EXAMPLE
a(1) = 6 = (2*3)/1;
a(2) = 20 = (4*5*6)/(2*3), etc.
MATHEMATICA
Floor[(#[[1]]!*#[[3]]!)/(#[[2]]!)^2]&/@Partition[Accumulate[ Range[ 0, 50]], 3, 1] (* Harvey P. Dale, Aug 21 2015 *)
CROSSREFS
Sequence in context: A369348 A143711 A338120 * A068377 A002943 A009946
KEYWORD
nonn
AUTHOR
Amarnath Murthy, Nov 09 2002
EXTENSIONS
More terms from Mark Hudson (mrmarkhudson(AT)hotmail.com), Feb 11 2003
Definition clarified by Harvey P. Dale, Aug 21 2015
STATUS
approved

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Last modified July 18 00:08 EDT 2024. Contains 374377 sequences. (Running on oeis4.)