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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

Table of n, a(n) for n=1..43.

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: A031052 A097811 A143711 * A002943 A068377 A009946

Adjacent sequences:  A077536 A077537 A077538 * A077540 A077541 A077542

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 August 22 02:44 EDT 2019. Contains 326169 sequences. (Running on oeis4.)