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 A081347 First column in maze arrangement of natural numbers. 4
 1, 2, 3, 12, 13, 30, 31, 56, 57, 90, 91, 132, 133, 182, 183, 240, 241, 306, 307, 380, 381, 462, 463, 552, 553, 650, 651, 756, 757, 870, 871, 992, 993, 1122, 1123, 1260, 1261, 1406, 1407, 1560, 1561, 1722, 1723, 1892, 1893, 2070, 2071, 2256, 2257, 2450, 2451 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,2 COMMENTS Interleaves two times the hexagonal numbers A000384 with A054554. LINKS Vincenzo Librandi, Table of n, a(n) for n = 0..1000 Index entries for linear recurrences with constant coefficients, signature (1,2,-2,-1,1). FORMULA a(n) = ((1+2*n^2)+(1-2*n)*(-1)^n)/2. a(2n) = A054554(n). a(2n+1) = 2*A000384(n). G.f.: (1+x-x^2+7*x^3)/((1-x)^3*(1+x)^2). [Colin Barker, Apr 17 2012] EXAMPLE Starting with 1,2,3, turn (LL) and then repeat (RRR)(LLL) to get 1 6 7 20 2 5 8 19 3 4 9 18 12 11 10 17 MATHEMATICA CoefficientList[Series[(1 + x - x^2 + 7 x^3) / ((1 - x)^3 (1 + x)^2), {x, 0, 50}], x] (* Vincenzo Librandi, Aug 08 2013 *) PROG (MAGMA) [((1+2*n^2)+(1-2*n)*(-1)^n)/2: n in [0..50]]; // Vincenzo Librandi, Aug 08 2013 CROSSREFS Cf. A081348, A080335. Sequence in context: A157900 A157902 A102660 * A309176 A074347 A102034 Adjacent sequences:  A081344 A081345 A081346 * A081348 A081349 A081350 KEYWORD easy,nonn AUTHOR Paul Barry, Mar 19 2003 STATUS approved

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Last modified June 20 04:43 EDT 2021. Contains 345157 sequences. (Running on oeis4.)