login

Year-end appeal: Please make a donation to the OEIS Foundation to support ongoing development and maintenance of the OEIS. We are now in our 61st year, we have over 378,000 sequences, and we’ve reached 11,000 citations (which often say “discovered thanks to the OEIS”).

A261359
Pentatope of coefficients in expansion of (1 + x + 2*y + 2*z)^n.
2
1, 1, 1, 2, 2, 1, 2, 4, 4, 1, 4, 4, 4, 8, 4, 1, 3, 6, 6, 3, 12, 12, 12, 24, 12, 1, 6, 6, 12, 24, 12, 8, 24, 24, 8, 1, 4, 8, 8, 6, 24, 24, 24, 48, 24, 4, 24, 24, 48, 96, 48, 32, 96, 96, 32, 1, 8, 8, 24, 48, 24, 32, 96, 96, 32, 16, 64, 96, 64, 16, 1, 5, 10, 10, 10, 40, 40, 40, 80, 40, 10, 60, 60, 120, 240, 120, 80, 240, 240, 80, 5, 40, 40, 120, 240, 120, 160, 480, 480, 160, 80, 320, 480, 320, 80, 1, 10, 10, 40, 80, 40, 80, 240, 240, 80, 80, 320, 480, 320, 80, 32, 160, 320, 320, 160, 32
OFFSET
0,4
COMMENTS
T(n,i,j,k) is the number of lattice paths from (0,0,0,0) to (n,i,j,k) with steps (1,0,0,0), (1,1,0,0) and two kinds of steps (1,1,1,0) and (1,1,1,1).
The sum of the numbers in each cell of the pentatope is 6^n (A000400).
FORMULA
T(i+1,j,k,l) = 2*T(i,j-1,k-1,l-1) + 2*T(i,j-1,k-1,l) + T(i,j-1,k,l) + T(i,j,k,l); T(i,j,k,-1)=0,...; T(0,0,0,0)=1.
T(n,i,j,k) = 2^j*binomial(n,i)*binomial(i,j)*binomial(j,k). - Dimitri Boscainos, Aug 21 2015
EXAMPLE
The 5th slice (n=4) of this 4D simplex starts at a(35). It comprises a 3D tetrahedron of 35 terms whose sum is 1296. It is organized as follows:
.
. 1
.
. 4
. 8 8
.
. 6
. 24 24
. 24 48 24
.
. 4
. 24 24
. 48 96 48
. 32 96 96 32
.
. 1
. 8 8
. 24 48 24
. 32 96 96 32
. 16 64 96 64 16
MAPLE
p:= proc(i, j, k, l) option remember;
if l<0 or j<0 or i<0 or i>l or j>i or k<0 or k>j then 0
elif {i, j, k, l}={0} then 1
else p(i, j, k, l-1) +p(i-1, j, k, l-1) +2*p(i-1, j-1, k, l-1)+2*p(i-1, j-1, k-1, l-1)
fi
end:
seq(seq(seq(seq(p(i, j, k, l), k=0..j), j=0..i), i=0..l), l=0..5);
# Adapted from Alois P. Heinz's Maple program for A261356
PROG
(PARI) lista(nn) = {for (n=0, nn, for (i=0, n, for (j=0, i, for (k=0, j, print1(2^j*binomial(n, i)*binomial(i, j)*binomial(j, k), ", ")); ); ); ); } \\ Michel Marcus, Oct 07 2015
CROSSREFS
KEYWORD
nonn,tabf,walk,less
AUTHOR
Dimitri Boscainos, Aug 16 2015
STATUS
approved