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%I #21 Aug 26 2017 07:44:46
%S 2,2,4,16,32,128,1024,4096,32768,524288,4194304,67108864,2147483648,
%T 34359738368,1099511627776,70368744177664,2251799813685248,
%U 144115188075855872,18446744073709551616,1180591620717411303424,151115727451828646838272
%N Number of n X n X n triangular binary arrays symmetric under rotations of 120 degrees.
%F a(n) = 2^ceiling(n(n+1)/6). - _Giovanni Resta_, Aug 23 2017
%e All solutions for n = 3:
%e 0 0 1 1
%e 0 0 1 1 0 0 1 1
%e 0 0 0 0 1 0 1 0 1 1 1 1
%t Table[2^Ceiling[n (n + 1)/6], {n, 20}] (* _Giovanni Resta_, Aug 23 2017 *)
%o (PARI) a(n) = 2^ceil(n*(n+1)/6) \\ after Giovanni Resta's formula
%Y Cf. A166197, A166198, A166199, A166200, A166201, A166202, A166203, A166204, A166205, A166206, A166207, A166208, A166209, A166210, A166211, A166212, A166213, A166214, A166215, A166216, A166217, A166218, A166219, A166220, A166221, A166222, A166223, A166224.
%K nonn,easy
%O 1,1
%A _Felix Fröhlich_, Aug 22 2017
%E More terms from _Giovanni Resta_, Aug 23 2017