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A049453
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Second pentagonal numbers with even index.
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15
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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; refs; listen; history; internal format)
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OFFSET
| 0,2
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COMMENTS
| 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
Sequence found by reading the line (one of the diagonal axes) from 0, in the direction 0, 7,..., in the square spiral whose vertices are the generalized pentagonal numbers A001318. - Omar E. Pol, Sep 08 2011
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FORMULA
| a(n) = n*(6*n+1).
G.f.: x*(7+5*x)/(1-x)^3.
a(n) = 12*n+a(n-1)-5 (with a(0)=0). - Vincenzo Librandi, Aug 06 2010
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MAPLE
| seq(binomial(6*n+1, 2)/3, n=0..42); - Zerinvary Lajos (zerinvarylajos(AT)yahoo.com), Jan 21 2007
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MATHEMATICA
| 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
| Cf. A005449, A033568, A049452.
Cf. A194454.
Cf. A001318, A033570, A049453. - Omar E. Pol, Sep 08 2011
Cf. A185019.
Sequence in context: A063159 A059376 A206481 * A171340 A046433 A128972
Adjacent sequences: A049450 A049451 A049452 * A049454 A049455 A049456
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KEYWORD
| nonn,easy
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AUTHOR
| Joe Keane (jgk(AT)jgk.org).
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