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Search: id:A011848
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| 0, 0, 0, 1, 3, 5, 7, 10, 14, 18, 22, 27, 33, 39, 45, 52, 60, 68, 76, 85, 95, 105, 115, 126, 138, 150, 162, 175, 189, 203, 217, 232, 248, 264, 280, 297, 315, 333, 351, 370, 390, 410, 430, 451, 473, 495, 517, 540, 564, 588, 612, 637, 663, 689, 715, 742, 770, 798
(list; graph; listen)
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OFFSET
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0,5
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FORMULA
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G.f.: x^3(1-x^2)/((1-x)^3(1-x^4)).
G.f.: x^3/(1+x^2)(1-x)^3 - Jon Perry (perry(AT)globalnet.co.uk), Mar 31 2004
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MAPLE
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seq(floor(binomial(n, 2)/2), n=0..57); # [From Zerinvary Lajos (zerinvarylajos(AT)yahoo.com), Jan 12 2009]
seq(floor(binomial(n, 2)/2) , n=0..57); # [From Zerinvary Lajos (zerinvarylajos(AT)yahoo.com), Jan 12 2009]
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PROGRAM
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(PARI) a(n)=binomial(n, 2)\2
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CROSSREFS
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A054925(n)=a(-n). A035608(n)=a(2n+1).
A column of triangle A011857.
First differences are in A004524.
Sequence in context: A057672 A112509 A054040 this_sequence A131673 A151945 A140261
Adjacent sequences: A011845 A011846 A011847 this_sequence A011849 A011850 A011851
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KEYWORD
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nonn
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AUTHOR
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N. J. A. Sloane (njas(AT)research.att.com).
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