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A050442
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Octahedral torus number: a(n) = n^2+2*sum(k^2,k=1..n-1)-2*(floor((n+1)/2)^2+2*sum(k^2,k=1..floor((n+1)/2)-1))+(1-(-1)^n)/2.
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0
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0, 4, 8, 32, 48, 108, 144, 256, 320, 500, 600, 864, 1008, 1372, 1568, 2048, 2304, 2916, 3240, 4000, 4400, 5324, 5808, 6912, 7488, 8788, 9464, 10976, 11760, 13500, 14400, 16384, 17408, 19652, 20808, 23328, 24624, 27436, 28880, 32000, 33600, 37044
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,2
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COMMENTS
| a(n) = A005900(n)-2*A005900(floor((n+1)/2))+(1-(-1)^n)/2
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LINKS
| Vincenzo Librandi, Table of n, a(n) for n = 1..1000
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FORMULA
| a(n) = (2*n^3+n)/3-2/3*(2*floor((n+1)/2)^3+floor((n+1)/2))+(1-(-1)^n)/2.
G.f.: 4*x^2*(1+x+3*x^2+x^3)/(1-x)^4/(1+x)^3. - Colin Barker, Feb 12 2012
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PROG
| (MAGMA) [(2*n^3+n)/3-2/3*(2*Floor((n+1)/2)^3+Floor((n+1)/2))+(1-(-1)^n)/2: n in [1..50]]; // Vincenzo Librandi, Feb 12 2012
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CROSSREFS
| Cf. A005900.
Sequence in context: A124143 A173617 A034041 * A094015 A094867 A149093
Adjacent sequences: A050439 A050440 A050441 * A050443 A050444 A050445
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KEYWORD
| nonn,easy,nice,changed
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AUTHOR
| Klaus Strassburger (strass(AT)ddfi.uni-duesseldorf.de), Dec 23 1999
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