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Search: id:A062123
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| 2, 11, 29, 56, 92, 137, 191, 254, 326, 407, 497, 596, 704, 821, 947, 1082, 1226, 1379, 1541, 1712, 1892, 2081, 2279, 2486, 2702, 2927, 3161, 3404, 3656, 3917, 4187, 4466, 4754, 5051, 5357, 5672, 5996, 6329, 6671, 7022, 7382, 7751, 8129, 8516, 8912, 9317
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OFFSET
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0,1
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COMMENT
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Third column of A046741.
Except for the first term, a(n)=9*n+a(n-1), (with a(1)=11) [From Vincenzo Librandi (vincenzo.librandi(AT)tin.it), Oct 24 2009]
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REFERENCES
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I. P. Goulden and D. M. Jackson, Combinatorial Enumeration, Wiley, N.Y., 1983,(2.3.14).
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LINKS
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Harry J. Smith, Table of n, a(n) for n=0,...,1000
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FORMULA
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G.f.: (1+2*x)*(2+x)/(1-x)^3. Generally, g.f. for k-th column of A046741 is coefficient of y^k in expansion of (1-y)/((1-y-y^2)*(1-y)-(1+y)*x).
a(n)=9*n+a(n-1)-9 (with a(1)=2) [From Vincenzo Librandi (vincenzo.librandi(AT)tin.it), Nov 18 2009]
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EXAMPLE
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For n=2, a(2)=9*2+2-9=11: n=3, a(3)=9*3+11-9=29; n=4, a(4)=9*4+29-9=56 [From Vincenzo Librandi (vincenzo.librandi(AT)tin.it), Nov 18 2009]
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PROGRAM
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(PARI) { for (n=0, 1000, write("b062123.txt", n, " ", 2 + (n + n^2)*9/2) ) } [From Harry J. Smith (hjsmithh(AT)sbcglobal.net), Aug 02 2009]
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CROSSREFS
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Cf. dumbbells: A002940, A002941, A002889, A046741, A055608, A062124-A062127.
Sequence in context: A090389 A061238 A046500 this_sequence A117560 A024178 A009312
Adjacent sequences: A062120 A062121 A062122 this_sequence A062124 A062125 A062126
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KEYWORD
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easy,nonn
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AUTHOR
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Vladeta Jovovic (vladeta(AT)eunet.rs), Jun 04 2001
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EXTENSIONS
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More terms from Larry Reeves (larryr(AT)acm.org), Jun 06 2001
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