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 A071231 a(n) = (n^8 + n^4)/2. 3
 0, 1, 136, 3321, 32896, 195625, 840456, 2883601, 8390656, 21526641, 50005000, 107186761, 215001216, 407879641, 737913736, 1281470625, 2147516416, 3487920481, 5510032776, 8491846681, 12800080000, 18911526921, 27438053896, 39155632561, 55037822976 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,3 COMMENTS Number of unoriented rows of length 8 using up to n colors. For a(0)=0, there are no rows using no colors. For a(1)=1, there is one row using that one color for all positions. For a(2)=136, there are 2^8=256 oriented arrangements of two colors. Of these, 2^4=16 are achiral. That leaves (256-16)/2=120 chiral pairs. Adding achiral and chiral, we get 136. - Robert A. Russell, Nov 13 2018 REFERENCES T. A. Gulliver, Sequences from Arrays of Integers, Int. Math. Journal, Vol. 1, No. 4, pp. 323-332, 2002. LINKS Vincenzo Librandi, Table of n, a(n) for n = 0..2000 Index entries for linear recurrences with constant coefficients, signature (9, -36, 84, -126, 126, -84, 36, -9, 1). FORMULA From Harvey P. Dale, Oct 11 2011: (Start) a(n) = 9*a(n-1) - 36*a(n-2) + 84*a(n-3) - 126*a(n-4) + 126*a(n-5) - 84*a(n-6) + 36*a(n-7) - 9*a(n-8) + a(n-9); a(0)=0, a(1)=1, a(2)=136, a(3)=3321, a(4)=32896, a(5)=195625, a(6)=840456, a(7)=2883601, a(8)=8390656. G.f.: -((x*(x+1)*(x*(x*(x*(x*(x*(x+126)+2007)+5812)+2007)+126)+1))/ (x-1)^9). (End) From Robert A. Russell, Nov 13 2018: (Start) a(n) = (A001016(n) + A000583(n)) / 2 = (n^8 + n^4) / 2. G.f.: (Sum_{j=1..8} S2(8,j)*j!*x^j/(1-x)^(j+1) + Sum_{j=1..4} S2(4,j)*j!*x^j/(1-x)^(j+1)) / 2, where S2 is the Stirling subset number A008277. G.f.: x*Sum_{k=0..7} A145882(8,k) * x^k / (1-x)^9. E.g.f.: (Sum_{k=1..8} S2(8,k)*x^k + Sum_{k=1..4} S2(4,k)*x^k) * exp(x) / 2, where S2 is the Stirling subset number A008277. For n>8, a(n) = Sum_{j=1..9} -binomial(j-10,j) * a(n-j). (End) E.g.f.: x*(2 + 134*x + 972*x^2 + 1702*x^3 + 1050*x^4 + 266*x^5 + 28*x^6 + x^7)*exp(x)/2. - G. C. Greubel, Nov 15 2018 MATHEMATICA Table[(n^8+n^4)/2, {n, 0, 30}] (* or *) LinearRecurrence[{9, -36, 84, -126, 126, -84, 36, -9, 1}, {0, 1, 136, 3321, 32896, 195625, 840456, 2883601, 8390656}, 30] (* Harvey P. Dale, Oct 11 2011 *) PROG (MAGMA) [(n^8 + n^4)/2: n in [0..50]]; // Vincenzo Librandi, Jun 14 2011 (PARI) vector(50, n, n--; (n^8 + n^4)/2) \\ G. C. Greubel, Nov 15 2018 (Sage) [(n^4 + n^8)/2 for n in range(50)] # G. C. Greubel, Nov 15 2018 (GAP) List([0..50], n -> (n^4 + n^8)/2); # G. C. Greubel, Nov 15 2018 CROSSREFS Row 8 of A277504. Cf. A001016 (oriented), A000583 (achiral). Subsequence of A000217 (triangular numbers). Sequence in context: A333110 A250424 A251940 * A233102 A249237 A194014 Adjacent sequences:  A071228 A071229 A071230 * A071232 A071233 A071234 KEYWORD nonn,easy AUTHOR N. J. A. Sloane, Jun 11 2002 STATUS approved

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Last modified April 10 11:15 EDT 2021. Contains 342845 sequences. (Running on oeis4.)