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
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