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 A342719 Array read by ascending antidiagonals: T(k, n) is the sum of the consecutive positive integers from 1 to (n - 1)*k placed along the perimeter of a n-th order perimeter-magic k-gon. 2
 21, 36, 45, 55, 78, 78, 78, 120, 136, 120, 105, 171, 210, 210, 171, 136, 231, 300, 325, 300, 231, 171, 300, 406, 465, 465, 406, 300, 210, 378, 528, 630, 666, 630, 528, 378, 253, 465, 666, 820, 903, 903, 820, 666, 465, 300, 561, 820, 1035, 1176, 1225, 1176, 1035, 820, 561 (list; table; graph; refs; listen; history; text; internal format)
 OFFSET 3,1 LINKS Terrel Trotter, Perimeter-Magic Polygons, Journal of Recreational Mathematics Vol. 7, No. 1, 1974, pp. 14-20 (see equation 3). FORMULA O.g.f.: (x^2 - 3*x^2*y + x*y^2 + 3*x^2*y^2)/((1 - x)^3*(1 - y)^3). E.g.f.: exp(x+y)*x*(x - x*y + y^2 + x*y^2)/2. T(k, n) = (n - 1)*k*((n - 1)*k + 1)/2. EXAMPLE The array begins: k\n|   3    4    5    6    7 ... ---+------------------------ 3  |  21   45   78  120  171 ... 4  |  36   78  136  210  300 ... 5  |  55  120  210  325  465 ... 6  |  78  171  300  465  666 ... 7  | 105  231  406  630  903 ... ... MATHEMATICA T[k_, n_]:=(n-1)k((n-1)k+1)/2; Table[T[k+3-n, n], {k, 3, 12}, {n, 3, k}]//Flatten CROSSREFS Cf. A014105 (n = 3), A033585 (n = 5), A037270 (1st superdiagonal), A081266 (n = 4), A083374 (1st subdiagonal), A110450 (diagonal), A144312 (n = 6), A144314 (n = 7), A342757, A342758. Sequence in context: A301963 A219919 A219215 * A155710 A001491 A112352 Adjacent sequences:  A342716 A342717 A342718 * A342720 A342721 A342722 KEYWORD nonn,tabl AUTHOR Stefano Spezia, Mar 19 2021 STATUS approved

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Last modified July 26 17:37 EDT 2021. Contains 346294 sequences. (Running on oeis4.)