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 A316725 Generalized 27-gonal (or icosiheptagonal) numbers: m*(25*m - 23)/2 with m = 0, +1, -1, +2, -2, +3, -3, ... 29
 0, 1, 24, 27, 73, 78, 147, 154, 246, 255, 370, 381, 519, 532, 693, 708, 892, 909, 1116, 1135, 1365, 1386, 1639, 1662, 1938, 1963, 2262, 2289, 2611, 2640, 2985, 3016, 3384, 3417, 3808, 3843, 4257, 4294, 4731, 4770, 5230, 5271, 5754, 5797, 6303, 6348, 6877, 6924, 7476, 7525, 8100, 8151, 8749, 8802 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,3 COMMENTS Note that in the sequences of generalized k-gonal numbers always a(3) = k. In this case k = 27. Generalized k-gonal numbers are second k-gonal numbers and positive terms of k-gonal numbers interleaved, with k >= 5. A general formula for the generalized k-gonal numbers is given by m*((k-2)*m-k+4)/2, with m = 0, +1, -1, +2, -2, +3, -3, ..., k >= 5. Partial sums of A317323. - Omar E. Pol, Jul 28 2018 LINKS Colin Barker, Table of n, a(n) for n = 0..1000 Index entries for linear recurrences with constant coefficients, signature (1,2,-2,-1,1). FORMULA From Colin Barker, Jul 11 2018: (Start) G.f.: x*(1 + 23*x + x^2) / ((1 - x)^3*(1 + x)^2). a(n) = n*(25*n + 46)/8 for n even. a(n) = (25*n - 21)*(n + 1)/8 for n odd. a(n) = a(n-1) + 2*a(n-2) - 2*a(n-3) - a(n-4) + a(n-5) for n>4. (End) MAPLE a:= n-> (m-> m*(25*m-23)/2)(-ceil(n/2)*(-1)^n): seq(a(n), n=0..60);  # Alois P. Heinz, Jul 11 2018 MATHEMATICA CoefficientList[Series[-x (x^2 + 23x + 1)/((x - 1)^3 (x + 1)^2), {x, 0, 53}], x] (* or *) LinearRecurrence[{1, 2, -2, -1, 1}, {0, 1, 24, 27, 73, 78, 147}, 53] (* Robert G. Wilson v, Jul 28 2018; corrected by Georg Fischer, Apr 03 2019 *) nn=30; Sort[Table[n (25 n - 23) / 2, {n, -nn, nn}]] (* Vincenzo Librandi, Jul 29 2018 *) PROG (PARI) concat(0, Vec(x*(1 + 23*x + x^2) / ((1 - x)^3*(1 + x)^2) + O(x^40))) \\ Colin Barker, Jul 11 2018 (GAP) a:=[0, 1, 24, 27, 73];;  for n in [6..60] do a[n]:=a[n-1]+2*a[n-2]-2*a[n-3]-a[n-4]+a[n-5]; od; a; # Muniru A Asiru, Jul 16 2018 CROSSREFS Cf. A255186; A317323. Sequences of generalized k-gonal numbers: A001318 (k=5), A000217 (k=6), A085787 (k=7), A001082 (k=8), A118277 (k=9), A074377 (k=10), A195160 (k=11), A195162 (k=12), A195313 (k=13), A195818 (k=14), A277082 (k=15), A274978 (k=16), A303305 (k=17), A274979 (k=18), A303813 (k=19), A218864 (k=20), A303298 (k=21), A303299 (k=22), A303303 (k=23), A303814 (k=24), A303304 (k=25), A316724 (k=26), this sequence (k=27), A303812 (k=28), A303815 (k=29), A316729 (k=30). Sequence in context: A162465 A067193 A095235 * A164778 A268540 A030500 Adjacent sequences:  A316722 A316723 A316724 * A316726 A316727 A316728 KEYWORD nonn,easy AUTHOR Omar E. Pol, Jul 11 2018 STATUS approved

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Last modified March 31 18:53 EDT 2020. Contains 333151 sequences. (Running on oeis4.)