OFFSET
0,3
LINKS
Alois P. Heinz, Table of n, a(n) for n = 0..60
MAPLE
b:= proc(n, p) option remember; `if`(p[4]>n, 0, `if`(n=0, 1,
add(add(add(add(b(n-1, sort(map(abs, p+[i, j, k, m])))
, i=-1..1), j=-1..1), k=-1..1), m=-1..1)))
end:
a:= n-> b(n, [0$2, 1$2]):
seq(a(n), n=0..20); # Alois P. Heinz, Dec 02 2012
MATHEMATICA
b[n_, p_] := b[n, p] = If[p[[4]] > n, 0, If[n == 0, 1,
Sum[Sum[Sum[Sum[b[n-1, Sort[Abs[ p + {i, j, k, m}]]],
{i, -1, 1}], {j, -1, 1}], {k, -1, 1}], {m, -1, 1}]]];
a[n_] := b[n, {0, 0, 1, 1}];
Table [a[n], {n, 0, 20}] (* Jean-François Alcover, Apr 28 2022, after Alois P. Heinz *)
PROG
(JavaScript)
b=new Array();
for (i1=-1; i1<2; i1++)
for (i2=-1; i2<2; i2++)
for (i3=-1; i3<2; i3++)
for (i4=-1; i4<2; i4++) {
n=(i1+1)+(i2+1)*3+(i3+1)*9+(i4+1)*27;
b[n]=[i1, i2, i3, i4];
}
function inc(arr, m) {
al=arr.length-1;
full=true;
for (ac=0; ac<=al; ac++) if (arr[ac]!=m) {full=false; break; }
if (full==true) return false;
while (arr[al]==m && al>0) {arr[al]=0; al--; }
arr[al]++;
return true;
}
for (k=0; k<5; k++) {
c=0;
a=new Array();
for (i=0; i<k; i++) a[i]=0;
for (i=0; i<Math.pow(81, k); i++) {
p=[0, 0, 0, 0];
for (j=0; j<k; j++) {p[0]+=b[a[j]][0]; p[1]+=b[a[j]][1]; p[2]+=b[a[j]][2]; p[3]+=b[a[j]][3]; }
if (p[0]==1 && p[1]==0 && p[2]==0 && p[3]==1) c++;
inc(a, 80);
}
document.write(c+", ");
}
CROSSREFS
KEYWORD
nonn
AUTHOR
Jon Perry, Dec 02 2012
EXTENSIONS
More terms from Alois P. Heinz, Dec 02 2012
STATUS
approved