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 A060549 a(n) is the number of distinct patterns (modulo geometric D3-operations) with strict median-reflective (palindrome) symmetry (i.e., having no other symmetry) which can be formed by an equilateral triangular arrangement of closely packed black and white cells satisfying the local matching rule of Pascal's triangle modulo 2, where n is the number of cells in each edge of the arrangement. The matching rule is such that any elementary top-down triangle of three neighboring cells in the arrangement contains either one or three white cells. 1
 0, 1, 2, 2, 6, 6, 12, 14, 28, 28, 60, 60, 120, 124, 248, 248, 504, 504, 1008, 1016, 2032, 2032, 4080, 4080, 8160, 8176, 16352, 16352, 32736, 32736, 65472, 65504, 131008, 131008, 262080, 262080, 524160, 524224, 1048448, 1048448, 2097024, 2097024 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,3 LINKS Harry J. Smith, Table of n, a(n) for n=1..500 A. Barbé, Symmetric patterns in the cellular automaton that generates Pascal's triangle modulo 2, Discr. Appl. Math. 105(2000), 1-38. FORMULA a(n) = 2^ceiling(n/2) - 2^(floor((n+3)/6) + d(n)), with d(n)=1 if n mod 6=1 else d(n)=0. a(n) = A060546(n) - A060548(n) = 2^A008619(n-1) - 2^A008615(n+1), for n >= 1. Empirical g.f.: x^2*(2*x^4 + 2*x^3 + 2*x + 1) / ((2*x^2-1)*(2*x^6-1)). - Colin Barker, Aug 29 2013 PROG (PARI) { for (n=1, 500, write("b060549.txt", n, " ", 2^ceil(n/2) - 2^(floor((n + 3)/6) + (n%6==1))); ) } \\ Harry J. Smith, Jul 07 2009 CROSSREFS Cf. A060546, A060548, A008619, A008615. Sequence in context: A051548 A110660 A139550 * A228315 A120690 A165124 Adjacent sequences:  A060546 A060547 A060548 * A060550 A060551 A060552 KEYWORD easy,nonn AUTHOR André Barbé (Andre.Barbe(AT)esat.kuleuven.ac.be), Apr 03 2001 STATUS approved

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Last modified November 20 10:09 EST 2019. Contains 329334 sequences. (Running on oeis4.)