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Search: id:A049453
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| A049453 |
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Second pentagonal numbers with even index. |
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+0
9
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| 0, 7, 26, 57, 100, 155, 222, 301, 392, 495, 610, 737, 876, 1027, 1190, 1365, 1552, 1751, 1962, 2185, 2420, 2667, 2926, 3197, 3480, 3775, 4082, 4401, 4732, 5075, 5430, 5797, 6176, 6567, 6970, 7385, 7812, 8251, 8702, 9165, 9640, 10127, 10626
(list; graph; listen)
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OFFSET
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0,2
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COMMENT
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Number of edges in the join of the complete tripartite graph of order 3n and the cycle graph of order n, K_n,n,n * C_n - Roberto E. Martinez II (remartin(AT)fas.harvard.edu), Jan 07 2002
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FORMULA
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a(n) = n*(6*n+1).
G.f.: A(x) = x*(7+5*x)/(1-x)^3.
a(n)=12*n+a(n-1)-17 (with a(1)=0) [From Vincenzo Librandi (vincenzo.librandi(AT)tin.it), Nov 12 2009]
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EXAMPLE
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For n=2, a(2)=12*2+0-17=7; n=3, a(3)=12*3+7-17=26; n=4, a(4)=12*4+26-17=57 [From Vincenzo Librandi (vincenzo.librandi(AT)tin.it), Nov 12 2009]
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MAPLE
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seq(binomial(6*n+1, 2)/3, n=0..42); - Zerinvary Lajos (zerinvarylajos(AT)yahoo.com), Jan 21 2007
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MATHEMATICA
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s=0; lst={s}; Do[s+=n++ +7; AppendTo[lst, s], {n, 0, 7!, 12}]; lst [From Vladimir Orlovsky (4vladimir(AT)gmail.com), Nov 16 2008]
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CROSSREFS
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Cf. A005449, A033568, A049452.
Sequence in context: A063578 A063159 A059376 this_sequence A046433 A128972 A135300
Adjacent sequences: A049450 A049451 A049452 this_sequence A049454 A049455 A049456
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KEYWORD
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nonn,easy,new
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AUTHOR
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Joe Keane (jgk(AT)jgk.org).
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