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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.

%I A278619 #13 Dec 07 2016 11:08:31
%S A278619 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,
%T A278619 121,139,157,179,205,231,262,298,334,376,425,481,537,601,673,745,827,
%U A278619 921,1027,1133,1254,1393,1550,1707,1886,2091,2322,2553,2815,3113,3447,3781,4157,4582,5063,5600
%N 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.
%C A278619 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.
%C A278619 For the same idea but for an right triangle see A278645; for a square spiral see A278180.
%C A278619 It appears that the same idea for an isosceles triangle and also for a square array gives A030237.
%e A278619 Illustration of initial terms as a spiral:
%e A278619 .
%e A278619 .             18 - 15 - 12
%e A278619 .             /          \
%e A278619 .           22    3 - 2   10
%e A278619 .           /    /     \   \
%e A278619 .         26    4   1 - 1   8
%e A278619 .           \    \         /
%e A278619 .           31    5 - 6 - 7
%e A278619 .             \
%e A278619 .              36 - 42 - 49
%e A278619 .
%e A278619 a(16) = 36 because the sum of its two largest neighbors is 31 + 5 = 36.
%e A278619 a(17) = 42 because the sum of its two largest neighbors is 36 + 6 = 42.
%e A278619 a(18) = 49 because the sum of its two largest neighbors is 42 + 7 = 49.
%e A278619 a(19) = 56 because the sum of its two largest neighbors is 49 + 7 = 56.
%Y A278619 Cf. A030237, A274920, A274921, A278180, A278181, A278645.
%K A278619 nonn
%O A278619 0,3
%A A278619 _Omar E. Pol_, Nov 24 2016