cp's OEIS Frontend

A274920 Spiral constructed on the nodes of the triangular net in which each new term is the least nonnegative integers distinct from its neighbors.

%I A274920 #31 Nov 14 2016 13:12:55
%S A274920 0,1,2,1,2,1,2,0,2,0,1,0,2,0,1,0,2,0,1,2,1,0,1,2,0,2,1,0,1,2,0,2,1,0,
%T A274920 1,2,0,1,0,2,1,2,0,1,2,1,0,2,1,2,0,1,2,1,0,2,1,2,0,1,2,0,2,1,0,2,0,1,
%U A274920 2,0,1,0,2,1,0,2,0,1,2,0,1,0,2,1,0,2,0,1,2,0,1,2,1,0,2,1,0,1,2,0,1,2,0,2,1,0
%N A274920 Spiral constructed on the nodes of the triangular net in which each new term is the least nonnegative integers distinct from its neighbors.
%C A274920 The structure of the spiral has the following properties:
%C A274920 1) Positive terms are on the nodes of a hexagonal net.
%C A274920 2) Every 0 is surrounded by three equidistant 1's and three equidistant 2's.
%C A274920 3) Every 1 is surrounded by three equidistant 0's and three equidistant 2's.
%C A274920 4) Every 2 is surrounded by three equidistant 0's and three equidistant 1's.
%C A274920 5) Diagonals are periodic sequences with period 3 (A010872 and A080425).
%C A274920 For the connection with the structure of graphene see also A275606.
%F A274920 a(n) = A274921(n) - 1.
%e A274920 Illustration of initial terms as a spiral:
%e A274920 .
%e A274920 .                2 - 0 - 1 - 2 - 0 - 1
%e A274920 .               /                     \
%e A274920 .              0   1 - 2 - 0 - 1 - 2   0
%e A274920 .             /   /                 \   \
%e A274920 .            1   2   0 - 1 - 2 - 0   1   2
%e A274920 .           /   /   /             \   \   \
%e A274920 .          2   0   1   2 - 0 - 1   2   0   1
%e A274920 .         /   /   /   /         \   \   \   \
%e A274920 .        0   1   2   0   1 - 2   0   1   2   0
%e A274920 .       /   /   /   /   /     \   \   \   \   \
%e A274920 .      1   2   0   1   2   0 - 1   2   0   1   2
%e A274920 .       \   \   \   \   \         /   /   /   /
%e A274920 .        0   1   2   0   1 - 2 - 0   1   2   0
%e A274920 .         \   \   \   \             /   /   /
%e A274920 .          2   0   1   2 - 0 - 1 - 2   0   1
%e A274920 .           \   \   \                 /   /
%e A274920 .            1   2   0 - 1 - 2 - 0 - 1   2
%e A274920 .             \   \                     /
%e A274920 .              0   1 - 2 - 0 - 1 - 2 - 0
%e A274920 .               \
%e A274920 .                2 - 0 - 1 - 2 - 0 - 1
%e A274920 .
%Y A274920 Cf. A010872, A080425, A274820, A274821, A274921, A275606, A275610.
%K A274920 nonn
%O A274920 0,3
%A A274920 _Omar E. Pol_, Jul 11 2016