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A099966
Sequence of the next-to-last entries in the rows of A099964.
3
1, 1, 3, 6, 14, 39, 109, 313, 900, 2943, 10403, 36195, 127474, 447352, 1711141, 7234223, 29672119, 123515469, 511672779, 2123410053, 9349845765, 45883313142, 216991244323, 1041956760633, 4977352149113, 23819499579914
OFFSET
1,3
LINKS
MAPLE
with(linalg):rev:=proc(a) local n, p; n:=vectdim(a): p:=i->a[n+1-i]: vector(n, p) end: ps:=proc(a) local n, q; n:=vectdim(a): q:=i->sum(a[j], j=1..i): vector(n, q) end: pss:=proc(a) local n, q; n:=vectdim(a): q:=proc(i) if i<=n then sum(a[j], j=1..i) else sum(a[j], j=1..n) fi end: vector(n+1, q) end: tr:={seq(n*(n+1)/2, n=1..30)}: R[0]:=vector(1, 1): for n from 1 to 30 do if member(n, tr)=false then R[n]:=ps(rev(R[n-1])) else R[n]:=pss(rev(R[n-1])) fi od: seq(R[n][vectdim(R[n])-1], n=1..30); # Emeric Deutsch, Nov 16 2004
MATHEMATICA
triQ[n_] := Module[{k}, Reduce[n == k (k + 1)/2, k, Integers] =!= False];
row[0] = {1}; row[1] = {1, 1}; row[n_] := row[n] = (ro = Accumulate[ Reverse[ row[n - 1]]]; If[triQ[n], Append[ro, Last[ro]], ro]); a[n_] := row[n][[-2]]; Array[a, 26] (* Jean-François Alcover, Feb 13 2018 *)
PROG
(Haskell)
a099966 n = a099966_list !! (n-1)
a099966_list = map (last . init) $ tail a099964_tabf
-- Reinhard Zumkeller, May 02 2012
CROSSREFS
Sequence in context: A261436 A335580 A079003 * A101162 A274054 A059741
KEYWORD
nonn,easy
AUTHOR
N. J. A. Sloane, Nov 13 2004
EXTENSIONS
More terms from Emeric Deutsch, Nov 16 2004
Offset corrected by Reinhard Zumkeller, May 02 2012
STATUS
approved