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 A120872 a(n) is the value of k for row n of the fixed-k dispersion for Q = 8. 0
 2, 1, 7, 4, 14, 9, 16, 7, 25, 14, 23, 8, 34, 17, 47, 28, 41, 18, 56, 31, 46, 17, 63, 32, 82, 49, 68, 31, 89, 50, 71, 28, 94, 49, 72, 23, 97, 46, 124, 71, 98, 41, 127, 68, 97, 34, 128, 63, 161, 94, 127, 56, 162, 89, 124, 47, 161, 82, 119, 36, 158, 73, 199, 112 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS This sequence results from A087059 by deleting duplicates. LINKS Clark Kimberling, The equation (j+k+1)^2 - 4*k = Q*n^2 and related dispersions, Journal of Integer Sequences, 10 (2007), Article #07.2.7. EXAMPLE For each positive integer n, there is a unique pair (j,k) of positive integers such that (j + k + 1)^2 - 4*k = 8*n^2. This representation is used to define the fixed-k dispersion for Q=8, given by A120861, having northwest corner:   1,  7,  41, 239, ...   2, 12,  70, 408, ...   3, 19, 111, 647, ...   4, 24, 140, 816, ...   ... The pair (j,k) for each n, shown in the position occupied by n in the above array, is shown here:   (1,2), (17,2),  (43,2),  (673,2), ...   (4,1), (32,1), (196,1), (1152,1), ...   (2,7), (46,7), (306,7), (1822,7), ...   (7,4), (63,4), (391,4), (2303,4), ...   ... The fixed-k for row 1 is a(1) = 2; the fixed-k for row 2 is a(2) = 1; etc. (For example, (46 + 7 + 1)^2 - 4*7 = 8*19^2.) PROG (PARI) f(n) = 3*n + 2*sqrtint(2*n^2) + 2; unused(listus) = {my(v=vecsort(Vec(listus))); for (i=1, vecmax(v), if (!vecsearch(v, i), return (i)); ); }; D(nb) = {my(m = matrix(nb, nb), t); my(listus = List); for (g=1, nb, if (g==1, t = 1, t = unused(listus)); m[g, 1]=t; listput(listus, t); t = f(t); m[g, 2]=t; listput(listus, t); for (h=3, nb, t = 6*m[g, h-1] - m[g, h-2]; m[g, h] = t; listput(listus, t); ); ); m; }; \\ A120860 q(n) = (1 + sqrtint(2*n^2))^2 - 2*n^2; \\ A087059 lista(nn) = my(m=D(nn)); vector(nn, n, q(m[n, 1])); \\ Michel Marcus, Jul 10 2020 CROSSREFS Cf. A087059, A120861. Sequence in context: A217458 A124048 A087059 * A204771 A141512 A143877 Adjacent sequences:  A120869 A120870 A120871 * A120873 A120874 A120875 KEYWORD nonn AUTHOR Clark Kimberling, Jul 10 2006 EXTENSIONS More terms from Michel Marcus, Jul 10 2020 STATUS approved

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Last modified November 28 18:39 EST 2021. Contains 349415 sequences. (Running on oeis4.)