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 A103470 Number of polyominoes without holes consisting of 4 regular unit n-gons. 11
 3, 5, 7, 7, 7, 11, 14, 19, 23, 23, 23, 29, 35, 42, 48, 47, 48, 57, 64, 74, 82, 81, 82, 93, 103, 115, 125, 123, 125, 139, 150, 165, 177, 175, 177, 193, 207, 224, 238, 235, 238, 257, 272, 292, 308, 305, 308, 329, 347, 369, 387, 383, 387, 411, 430, 455, 475, 471, 475 (list; graph; refs; listen; history; text; internal format)
 OFFSET 3,1 LINKS Colin Barker, Table of n, a(n) for n = 3..1000 S. Kurz, k-polyominoes. Index entries for linear recurrences with constant coefficients, signature (2,-2,2,-2,2,-1,0,0,0,0,0,1,-2,2,-2,2,-2,1). FORMULA See the link for a formula. G.f.: -x^3*(x^17 -2*x^16 +3*x^15 -4*x^14 +4*x^13 -4*x^12 +4*x^11 -2*x^10 +2*x^9 -2*x^8 +4*x^7 -x^6 +x^5 +3*x^4 -3*x^3 +3*x^2 -x +3) / ((x -1)^3*(x +1)*(x^2 -x +1)^2*(x^2 +1)*(x^2 +x +1)^2*(x^4 -x^2 +1)). - Colin Barker, Jan 19 2015 EXAMPLE a(3)=3 because there are 3 polyiamonds consisting of 4 triangles and a(4)=5 because there are 5 polyominoes consisting of 4 squares. MATHEMATICA LinearRecurrence[{2, -2, 2, -2, 2, -1, 0, 0, 0, 0, 0, 1, -2, 2, -2, 2, -2, 1}, {3, 5, 7, 7, 7, 11, 14, 19, 23, 23, 23, 29, 35, 42, 48, 47, 48, 57}, 80] (* Harvey P. Dale, Feb 11 2020 *) PROG (PARI) Vec(-x^3*(x^17 -2*x^16 +3*x^15 -4*x^14 +4*x^13 -4*x^12 +4*x^11 -2*x^10 +2*x^9 -2*x^8 +4*x^7 -x^6 +x^5 +3*x^4 -3*x^3 +3*x^2 -x +3)/((x -1)^3*(x +1)*(x^2 -x +1)^2*(x^2 +1)*(x^2 +x +1)^2*(x^4 -x^2 +1)) + O(x^100)) \\ Colin Barker, Jan 19 2015 CROSSREFS Cf. A103469, A103471, A103472, A103473. Sequence in context: A211517 A254935 A104199 * A316852 A307120 A261010 Adjacent sequences:  A103467 A103468 A103469 * A103471 A103472 A103473 KEYWORD nonn,easy AUTHOR Sascha Kurz, Feb 07 2005 STATUS approved

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Last modified August 13 00:27 EDT 2020. Contains 336441 sequences. (Running on oeis4.)