A099962 First column (also row sums) of triangle in A099961.

1, 1, 1, 1, 2, 3, 5, 13, 28, 64, 207, 578, 1685, 6518, 22361, 79319, 357180, 1453177, 6075215, 31216968, 146906126, 707344776, 4084254624, 21823224623, 118932148555, 762346849634, 4559139897594, 27742486678915, 195472113041924

Offset

0,5

Links

Table of n, a(n) for n=0..28.

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: R[0]:=vector(1, 1): for n from 1 to 35 do if n mod 3 = 0 or n mod 3 = 1 then R[n]:=ps(rev(R[n-1])) else R[n]:=pss(rev(R[n-1])) fi od: seq(R[n][1], n=0..35); # Emeric Deutsch, Nov 16 2004

Mathematica

r[n_] := r[n] = If[n == 0, {1}, Module[{a}, Join[a = Accumulate[Reverse[r[n-1]]], If[Mod[n, 3] == 2, {Last[a]}, {}]]]];
a[n_] := If[n == 0, 1, r[n][[1]]];
Table[a[n], {n, 0, 28}] (* Jean-François Alcover, Mar 10 2023 *)

Crossrefs

Cf. A099961.

Sequence in context: A357916 A289758 A089477 * A173718 A281316 A329241

Adjacent sequences: A099959 A099960 A099961 * A099963 A099964 A099965

Keyword

nonn,easy

Author

N. J. A. Sloane, Nov 13 2004

Extensions

More terms from Emeric Deutsch, Nov 16 2004

Status

approved