A278317 Number of neighbors of each new term in a right triangle read by rows.

0, 1, 2, 2, 3, 2, 2, 4, 3, 2, 2, 4, 4, 3, 2, 2, 4, 4, 4, 3, 2, 2, 4, 4, 4, 4, 3, 2, 2, 4, 4, 4, 4, 4, 3, 2, 2, 4, 4, 4, 4, 4, 4, 3, 2, 2, 4, 4, 4, 4, 4, 4, 4, 3, 2, 2, 4, 4, 4, 4, 4, 4, 4, 4, 3, 2, 2, 4, 4, 4, 4, 4, 4, 4, 4, 4, 3, 2, 2, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 3, 2, 2, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 3, 2

Offset

1,3

Comments

To evaluate T(n,k) consider only the neighbors of T(n,k) that are present in the triangle when T(n,k) should be a new term in the triangle.

Apart from the first column and the first two diagonals the rest of the elements are 4's.

For the same idea but for an isosceles triangle see A275015; for a square array see A278290, for a square spiral see A278354; and for a hexagonal spiral see A047931.

Links

Table of n, a(n) for n=1..105.

Example

Triangle begins:
0;
1, 2;
2, 3, 2;
2, 4, 3, 2;
2, 4, 4, 3, 2;
2, 4, 4, 4, 3, 2;
2, 4, 4, 4, 4, 3, 2;
2, 4, 4, 4, 4, 4, 3, 2;
2, 4, 4, 4, 4, 4, 4, 3, 2;
2, 4, 4, 4, 4, 4, 4, 4, 3, 2;
...

Crossrefs

Apart from the initial zero, row sums give A004767.

Column 1 is A130130.

Columns > 1 give the terms greater than 1 of A158411.

Right border gives 0 together with A007395, also twice A057427.

Second right border gives A122553.

Cf. A047931, A274912, A274913, A275015, A278290, A278317, A278354,

Sequence in context: A364925 A160651 A230296 * A086454 A339492 A069360

Adjacent sequences: A278314 A278315 A278316 * A278318 A278319 A278320

Keyword

nonn,tabl

Author

Omar E. Pol, Nov 18 2016

Status

approved