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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 (list; graph; refs; listen; history; text; internal format)
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-Fran├žois 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: A106395 A261436 A079003 * A101162 A274054 A059741

Adjacent sequences:  A099963 A099964 A099965 * A099967 A099968 A099969

KEYWORD

nonn,easy

AUTHOR

N. J. A. Sloane, Nov 13 2004, following a suggestion made by Douglas G. Rogers, Mar 10 2003

EXTENSIONS

More terms from Emeric Deutsch, Nov 16 2004

Offset corrected by Reinhard Zumkeller, May 02 2012

STATUS

approved

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Last modified July 21 04:40 EDT 2019. Contains 325189 sequences. (Running on oeis4.)