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A278619 Hexagonal spiral constructed on the nodes of the triangular net in which each new term is the sum of its two largest neighbors in the structure. 2
1, 1, 2, 3, 4, 5, 6, 7, 8, 10, 12, 15, 18, 22, 26, 31, 36, 42, 49, 56, 64, 72, 82, 94, 106, 121, 139, 157, 179, 205, 231, 262, 298, 334, 376, 425, 481, 537, 601, 673, 745, 827, 921, 1027, 1133, 1254, 1393, 1550, 1707, 1886, 2091, 2322, 2553, 2815, 3113, 3447, 3781, 4157, 4582, 5063, 5600 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,3

COMMENTS

To evaluate a(n) consider only the two largest neighbors of a(n) that are present in the spiral when a(n) should be a new term in the spiral.

For the same idea but for an right triangle see A278645; for a square spiral see A278180.

It appears that the same idea for an isosceles triangle and also for a square array gives A030237.

LINKS

Table of n, a(n) for n=0..60.

EXAMPLE

Illustration of initial terms as a spiral:

.

.             18 - 15 - 12

.             /          \

.           22    3 - 2   10

.           /    /     \   \

.         26    4   1 - 1   8

.           \    \         /

.           31    5 - 6 - 7

.             \

.              36 - 42 - 49

.

a(16) = 36 because the sum of its two largest neighbors is 31 + 5 = 36.

a(17) = 42 because the sum of its two largest neighbors is 36 + 6 = 42.

a(18) = 49 because the sum of its two largest neighbors is 42 + 7 = 49.

a(19) = 56 because the sum of its two largest neighbors is 49 + 7 = 56.

CROSSREFS

Cf. A030237, A274920, A274921, A278180, A278181, A278645.

Sequence in context: A029750 A266480 A246080 * A173925 A320319 A263363

Adjacent sequences:  A278616 A278617 A278618 * A278620 A278621 A278622

KEYWORD

nonn

AUTHOR

Omar E. Pol, Nov 24 2016

STATUS

approved

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Last modified October 17 17:21 EDT 2021. Contains 348065 sequences. (Running on oeis4.)