

A278180


Square spiral in which each new term is the sum of its two largest neighbors.


4



1, 1, 2, 3, 4, 7, 8, 15, 16, 17, 33, 35, 37, 72, 76, 80, 84, 164, 172, 180, 188, 368, 384, 401, 418, 435, 853, 888, 925, 962, 999, 1961, 2037, 2117, 2201, 2285, 2369, 4654, 4826, 5006, 5194, 5382, 5570, 10952, 11336, 11737, 12155, 12590, 13025, 13460, 26485, 27373, 28298, 29260, 30259, 31258, 32257, 63515
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OFFSET

1,3


COMMENTS

To evaluate a(n) consider the 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 a hexagonal spiral see A278619; and for a right triangle see A278645. It appears that the same idea for an isosceles triangle and also for a square array gives A030237.  Omar E. Pol, Dec 04 2016


LINKS

Table of n, a(n) for n=1..58.


EXAMPLE

Illustration of initial terms as a square spiral:
.
. 8480767237
.  
. 164 432 35
.    
. 172 7 11 33
.   
. 180 8151617
. 
. 188368384401418
.
a(21) = 188 because the sum of its two largest neighbors is 180 + 8 = 188.
a(22) = 368 because the sum of its two largest neighbors is 180 + 188 = 368.
a(23) = 384 because the sum of its two largest neighbors is 368 + 16 = 384.
a(24) = 401 because the sum of its two largest neighbors is 384 + 17 = 401.
a(25) = 418 because the sum of its two largest neighbors is 401 + 17 = 418.
a(26) = 435 because the sum of its two largest neighbors is 418 + 17 = 435.


CROSSREFS

Cf. A030237, A078510, A141481, A274917, A278181, A278619, A278645.
Sequence in context: A084541 A240690 A113050 * A015927 A097110 A116961
Adjacent sequences: A278177 A278178 A278179 * A278181 A278182 A278183


KEYWORD

nonn


AUTHOR

Omar E. Pol, Nov 14 2016


STATUS

approved



