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A291338
Number of n X n X n triangular binary arrays symmetric under rotations of 120 degrees.
0
2, 2, 4, 16, 32, 128, 1024, 4096, 32768, 524288, 4194304, 67108864, 2147483648, 34359738368, 1099511627776, 70368744177664, 2251799813685248, 144115188075855872, 18446744073709551616, 1180591620717411303424, 151115727451828646838272
OFFSET
1,1
FORMULA
a(n) = 2^ceiling(n(n+1)/6). - Giovanni Resta, Aug 23 2017
EXAMPLE
All solutions for n = 3:
0 0 1 1
0 0 1 1 0 0 1 1
0 0 0 0 1 0 1 0 1 1 1 1
MATHEMATICA
Table[2^Ceiling[n (n + 1)/6], {n, 20}] (* Giovanni Resta, Aug 23 2017 *)
PROG
(PARI) a(n) = 2^ceil(n*(n+1)/6) \\ after Giovanni Resta's formula
KEYWORD
nonn,easy
AUTHOR
Felix Fröhlich, Aug 22 2017
EXTENSIONS
More terms from Giovanni Resta, Aug 23 2017
STATUS
approved