This site is supported by donations to The OEIS Foundation.

 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 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: 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

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recent
The OEIS Community | Maintained by The OEIS Foundation Inc.

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