[seqfan] Re: The Bad Neighbors Sequence

[Ruud H.G. van Tol]

And now a more fundamental correction:

{ my(N=32, r=List(), v=vector(N,i,i), w=matrix(N,N,r,c,(r>1 && 
c==r-1)||(r<N && c==r+1)));
   while(1
   , my(p=v[1], q=3);
     listput(r, p);
     while(q < N && (w[v[q],p] || w[v[q+1],p]), q++);
     if(q < N
     , for(i=2,q, v[i-1]=v[i]);
       v[q]= p;
       w[p, v[q-1]]= w[p, v[q+1]]= w[v[q-1], p]= w[v[q+1], p]= 1;
     , listput(r, 0);
       break;
     );
   );
   Vec(r)
}

which produces:

1, 2, 3, 1, 4, 2, 5, 3, 6, 1, 5, 7, 4, 6, 8, 2, 7, 9, 3, 8, 10, 1, 9, 
11, 8, 5, 10, 12, 9, 4, 11, 13, 10, 2, 12, 6, 9, 14, 2, 11, 3, 13, 7, 
10, 6, 11, 15, 3, 12, 14, 8, 13, 1, 12, 16, 13, 9, 15, 13, 5, 14, 1, 17, 
10, 14, 16, 4, 15, 18, 16, 2, 15, 17, 19, 16, 11, 18, 7, 0


or reformatted:

_1,
_2,
_3,  1,
_4,  2,
_5,  3,
_6,  1,  5,
_7,  4,  6,
_8,  2,  7,
_9,  3,  8,
10,  1,  9,
11,  8,  5, 10,
12,  9,  4, 11,
13, 10,  2, 12,  6,  9,
14,  2, 11,  3, 13,  7, 10,  6, 11,
15,  3, 12, 14,  8, 13,  1, 12,
16, 13,  9, 15, 13,  5, 14,  1,
17, 10, 14, 16,  4, 15,
18, 16,  2, 15, 17,
19, 16, 11, 18,  7,
0

-- Ruud

P.S. Both previous versions were not checking enough neighbors.