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

Author

Alex Ratushnyak, Jul 07 2012

Keywords

• nonn
• easy

Comments

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

The central 1 is at ?

Examples

			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).