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Search: id:A139268
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| A139268 |
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Twice nonagonal numbers (or twice 9-gonal numbers): n(7n-5). |
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+0
3
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| 0, 2, 18, 48, 92, 150, 222, 308, 408, 522, 650, 792, 948, 1118, 1302, 1500, 1712, 1938, 2178, 2432, 2700, 2982, 3278, 3588, 3912, 4250, 4602, 4968, 5348, 5742, 6150, 6572, 7008, 7458, 7922, 8400, 8892, 9398, 9918, 10452, 11000
(list; graph; listen)
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OFFSET
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0,2
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FORMULA
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a(n) = A001106(n)*2 = 7*n^2-5*n = n(7n-5).
a(n)=14*n+a(n-1)-26 (with a(1)=0) [From Vincenzo Librandi (vincenzo.librandi(AT)tin.it), Nov 13 2009]
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EXAMPLE
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For n=2, a(2)=14*2+0-26=2; n=3, a(3)=14*3+2-26=18; n=4, a(4)=14*4+18-26=48 [From Vincenzo Librandi (vincenzo.librandi(AT)tin.it), Nov 13 2009]
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MATHEMATICA
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s=0; lst={s}; Do[s+=n; AppendTo[lst, s], {n, 2, 6!, 14}]; lst [From Vladimir Orlovsky (4vladimir(AT)gmail.com), Apr 02 2009]
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CROSSREFS
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Cf. A001106.
Sequence in context: A131538 A009820 A126909 this_sequence A052681 A048910 A077591
Adjacent sequences: A139265 A139266 A139267 this_sequence A139269 A139270 A139271
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KEYWORD
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easy,nonn,new
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AUTHOR
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Omar E. Pol (info(AT)polprimos.com), May 15 2008
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