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-1, 2, 6, 11, 17, 24, 32, 41, 51, 62, 74, 87, 101, 116, 132, 149, 167, 186, 206, 227, 249, 272, 296, 321, 347, 374, 402, 431, 461, 492, 524, 557, 591, 626, 662, 699, 737, 776, 816, 857, 899, 942, 986, 1031, 1077, 1124, 1172, 1221, 1271, 1322
(list; graph; refs; listen; history; internal format)
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OFFSET
| 0,2
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COMMENTS
| If Y_i (i=1,2,3,4) are 2-blocks of an n-set X then, for n>=8, a(n-3) is the number of (n-2)-subsets of X intersecting each Y_i (i=1,2,3,4). - Milan R. Janjic (agnus(AT)blic.net), Nov 09 2007
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LINKS
| Milan Janjic, Two Enumerative Functions
P. Di Francesco, O. Golinelli and E. Guitter, Meander, folding and arch statistics.
Index entries for sequences related to linear recurrences with constant coefficients, signature (3,-3,1).
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FORMULA
| G.f.: A(x) = (-1+5*x-3*x^2)/(1-x)^3.
a(n)=a(n-1)+n+2 (with a(0)=-1) [From Vincenzo Librandi, Nov 18 2010]
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MAPLE
| seq(binomial(n, 2)-4, n=3..52); - Zerinvary Lajos (zerinvarylajos(AT)yahoo.com), Jan 13 2007
with (combinat):seq((fibonacci(3, n)+n-9)/2, n=2..51); - Zerinvary Lajos (zerinvarylajos(AT)yahoo.com), Jun 07 2008
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MATHEMATICA
| i=3; s=-1; lst={}; Do[s+=n+i; If[s>=0, AppendTo[lst, s]], {n, 0, 6!, 1}]; lst [From Vladimir Orlovsky (4vladimir(AT)gmail.com), Oct 29 2008]
s=-1; lst={}; Do[s+=n-2; If[s>-2, AppendTo[lst, s]], {n, 0, 6!, 1}]; lst [From Vladimir Orlovsky (4vladimir(AT)gmail.com), Nov 04 2008]
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CROSSREFS
| Triangular numbers (A000217) minus 4. Cf. A027379.
Cf. A002522.
Sequence in context: A193910 A078476 A099056 * A098167 A081689 A176708
Adjacent sequences: A046688 A046689 A046690 * A046692 A046693 A046694
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KEYWORD
| sign,easy
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AUTHOR
| N. J. A. Sloane (njas(AT)research.att.com).
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