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A289761
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Maximum length of a perfect Wichmann ruler with n segments.
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7
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3, 6, 9, 12, 15, 22, 29, 36, 43, 50, 57, 68, 79, 90, 101, 112, 123, 138, 153, 168, 183, 198, 213, 232, 251, 270, 289, 308, 327, 350, 373, 396, 419, 442, 465, 492, 519, 546, 573, 600, 627, 658, 689, 720, 751, 782, 813, 848, 883, 918, 953, 988, 1023, 1062, 1101, 1140, 1179, 1218, 1257, 1300, 1343, 1386, 1429
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OFFSET
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2,1
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COMMENTS
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LINKS
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FORMULA
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a(n) = ( n^2 - (mod(n,6)-3)^2 ) / 3 + n.
G.f.: x^2*(3 + 4*x^5 - 3*x^6) / ((1 - x)^3*(1 + x)*(1 - x + x^2)*(1 + x + x^2)).
a(n) = 2*a(n-1) - a(n-2) + a(n-6) - 2*a(n-7) + a(n-8) for n>9.
(End)
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MATHEMATICA
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PROG
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(PARI) a(n) = n + (n^2 - (n%6 - 3)^2)/3; \\ Michel Marcus, Jul 14 2017
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CROSSREFS
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KEYWORD
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nonn,easy
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AUTHOR
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STATUS
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approved
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