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 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 (list; graph; refs; listen; history; text; internal format)
 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 EXAMPLE Illustration of initial terms as a square spiral: . .          84----80----76-----72----37 .           |                        | .          164    4-----3-----2     35 .           |     |           |      | .          172    7     1-----1     33 .           |     |                  | .          180    8-----15----16----17 .           | .          188---368---384---401---418 . 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

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Last modified December 16 01:32 EST 2019. Contains 330013 sequences. (Running on oeis4.)