A099966 Sequence of the next-to-last entries in the rows of A099964.

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

Reinhard Zumkeller, Table of n, a(n) for n = 1..750

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

Cf. A099964, A099965.

Sequence in context: A261436 A335580 A079003 * A101162 A274054 A059741

Adjacent sequences: A099963 A099964 A099965 * A099967 A099968 A099969

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