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Search: id:A028895
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| A028895 |
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5 times triangular numbers. |
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+0
9
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| 0, 5, 15, 30, 50, 75, 105, 140, 180, 225, 275, 330, 390, 455, 525, 600, 680, 765, 855, 950, 1050, 1155, 1265, 1380, 1500, 1625, 1755, 1890, 2030, 2175, 2325, 2480, 2640, 2805, 2975, 3150, 3330, 3515, 3705, 3900, 4100, 4305, 4515, 4730, 4950
(list; graph; listen)
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OFFSET
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0,2
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COMMENT
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Except for the first term, a(n)=5*n+a(n-1), (with a(1)=5) [From Vincenzo Librandi (vincenzo.librandi(AT)tin.it), Oct 24 2009]
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FORMULA
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a(n) = 5/2*n*(n+1). G.f.: A(x) = 5*x/(1-x)^3.
a(n) = (5n^2 + 5n)/2 = 5n(n+1)/2 = A000217(n)*5. [From Omar E. Pol (info(AT)polprimos.com), Dec 12 2008]
a(n)=5*n+a(n-1)-5 (with a(1)=0) [From Vincenzo Librandi (vincenzo.librandi(AT)tin.it), Nov 12 2009]
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EXAMPLE
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For n=2, a(2)=5*2+0-5=5; n=3, a(3)=5*3+5-5=15; n=4, a(4)=5*4+15-5=30 [From Vincenzo Librandi (vincenzo.librandi(AT)tin.it), Nov 12 2009]
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MAPLE
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[seq(5*binomial(n, 2), n=1..45)]; - Zerinvary Lajos (zerinvarylajos(AT)yahoo.com), Nov 24 2006
a:=n->sum(2*n+j, j=0..n): seq(a(n), n=0..44); - Zerinvary Lajos (zerinvarylajos(AT)yahoo.com), Apr 29 2007
with(finance):seq(add(cashflows([n, k, 0], 1 ), k=0..n)*4, n=0..45); # [From Zerinvary Lajos (zerinvarylajos(AT)yahoo.com), Dec 22 2008]
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MATHEMATICA
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s=0; lst={}; Do[s+=n; AppendTo[lst, s], {n, 0, 7!, 5}]; lst [From Vladimir Orlovsky (4vladimir(AT)gmail.com), Nov 19 2008]
Table[Sum[i + 2*n - 1, {i, 2, n}], {n, 1, 45}] [From Zerinvary Lajos (zerinvarylajos(AT)yahoo.com), Jul 11 2009]
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CROSSREFS
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Cf. A005891, A046092, A028896.
Cf. A000217. [From Omar E. Pol (info(AT)polprimos.com), Dec 12 2008]
Sequence in context: A162525 A078905 A059160 this_sequence A010898 A048065 A048021
Adjacent sequences: A028892 A028893 A028894 this_sequence A028896 A028897 A028898
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KEYWORD
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nonn,easy,new
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AUTHOR
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Joe Keane (jgk(AT)jgk.org)
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