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 A209978 a(n) = A196227(n)/2. 9
 0, 0, 1, 4, 7, 14, 17, 28, 35, 46, 53, 72, 79, 102, 113, 128, 143, 174, 185, 220, 235, 258, 277, 320, 335, 374, 397, 432, 455, 510, 525, 584, 615, 654, 685, 732, 755, 826, 861, 908, 939, 1018, 1041, 1124, 1163, 1210, 1253, 1344, 1375, 1458, 1497 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,4 COMMENTS See A210000 for a guide to related sequences. LINKS MAPLE a:= proc(n) option remember; `if`(n<2, 0, a(n-1)-1 + 2*numtheory[phi](n)) end: seq(a(n), n=0..60); # Alois P. Heinz, May 05 2020 MATHEMATICA a = 1; b = n; z1 = 50; t[n_] := t[n] = Flatten[Table[w*z - x*y, {w, a, b}, {x, a, b}, {y, a, b}, {z, a, b}]] c[n_, k_] := c[n, k] = Count[t[n], k] Table[c[n, 0], {n, 0, z1}] (* A134506 *) Table[c[n, 1], {n, 0, z1}] (* A196227 *) %/2 (* A209978 *) Table[2 c[n, 1], {n, 0, z1}](* A209979 *) Table[c[n, 2], {n, 0, z1}] (* A197168 *) %/2 (* A209980 *) Table[c[n, 3], {n, 0, z1}] (* A210001 *) Table[c[n, 4], {n, 0, z1}] (* A210002 *) Table[c[n, 5], {n, 0, z1}] (* A210027 *) CROSSREFS Cf. A196227, A210000. Sequence in context: A310910 A310911 A255649 * A294016 A344533 A310912 Adjacent sequences: A209975 A209976 A209977 * A209979 A209980 A209981 KEYWORD nonn AUTHOR Clark Kimberling, Mar 16 2012 STATUS approved

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Last modified February 5 20:57 EST 2023. Contains 360087 sequences. (Running on oeis4.)