A214227 Sum of the four nearest neighbors of n in a triangular spiral with positive integers.

24, 32, 20, 28, 56, 44, 64, 48, 60, 88, 60, 56, 60, 64, 68, 84, 128, 100, 92, 96, 136, 104, 108, 112, 132, 176, 132, 120, 124, 128, 132, 136, 140, 144, 148, 172, 232, 188, 172, 176, 180, 184, 240, 192, 196, 200, 204, 208, 236, 296, 236, 216, 220, 224, 228, 232, 236

Offset

1,1

Comments

Nearby numbers on diagonals are not counted as neighbors for this sequence.

The central 1 is at ?

Links

Table of n, a(n) for n=1..57.

Example

Triangular spiral begins:
.
                       43
                       / \
                      /   \
                    42 21 44
                    /  / \  \
                   /  /   \  \
                 41 20  7 22 45
                 /  /  / \  \  \
                /  /  /   \  \  \
              40 19  6  1  8 23 46
              /  /  /    \  \  \  \
             /  /  /      \  \  \  \
           39 18  5--4--3--2  9 24 47
           /  /                \  \  \
          /  /                  \  \  \
        38 17-16-15-14-13-12-11-10 25 48
        /                            \  \
       /                              \  \
     37-36-35-34-33-32-31-30-29-28-27-26 49
                                           \
                                            \
  64-63-62-61-60-59-58-57-56-55-54-53-52-51-50
.
The four nearest neighbors of 3 are 1, 4, 2, 13; their sum is a(3)=20.

Crossrefs

Cf. A214226 (sum of the 8 nearest neighbors).

Sequence in context: A206448 A266984 A217158 * A337055 A064673 A034782

Adjacent sequences: A214224 A214225 A214226 * A214228 A214229 A214230

Keyword

nonn,easy

Author

Alex Ratushnyak, Jul 07 2012

Status

approved