| 0, 0, 0, 0, 0, 1, 2, 3, 4, 5, 7, 9, 11, 13, 15, 18, 21, 24, 27, 30, 34, 38, 42, 46, 50, 55, 60, 65, 70, 75, 81, 87, 93, 99, 105, 112, 119, 126, 133, 140, 148, 156, 164, 172, 180, 189, 198, 207, 216, 225, 235, 245, 255, 265, 275, 286, 297, 308, 319, 330, 342, 354, 366
(list; graph; listen)
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OFFSET
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0,7
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COMMENT
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Complementary with A130483 regarding triangular numbers, in that A130483(n)+5*a(n)=n(n+1)/2=A000217(n).
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FORMULA
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a(n)=1/2*floor(n/5)*(2n-3-5*floor(n/5))=A002266(n)*(2n-3-5*A002266(n))/2. Also: a(n)=1/2*A002266(n)*(n-3+A010874(n)). G.f.: g(x)=x^5/((1-x^5)(1-x)^2).
a(n) = floor((n-1)(n-2)/10) [From Mitch Harris (maharri(AT)gmail.com), Sep 08 2008]
a(n)=A008732(n-5), n>4. [From R. J. Mathar (mathar(AT)strw.leidenuniv.nl), Nov 22 2008]
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CROSSREFS
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Cf. A002264, A002265, A004526, A010872, A010873, A010874, A130481, A130482.
Adjacent sequences: A130517 A130518 A130519 this_sequence A130521 A130522 A130523
Sequence in context: A051532 A135785 A008732 this_sequence A005706 A064175 A000028
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KEYWORD
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nonn
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AUTHOR
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Hieronymus Fischer (Hieronymus.Fischer(AT)gmx.de), Jun 01 2007
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