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Search: id:A087811
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| A087811 |
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Numbers n such that ceil(sqrt(n)) divides n. |
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+0
4
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| 1, 2, 4, 6, 9, 12, 16, 20, 25, 30, 36, 42, 49, 56, 64, 72, 81, 90, 100, 110, 121, 132, 144, 156, 169, 182, 196, 210, 225, 240, 256, 272, 289, 306, 324, 342, 361, 380, 400, 420, 441, 462, 484, 506, 529, 552, 576, 600, 625, 650, 676, 702, 729, 756, 784, 812, 841
(list; graph; listen)
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OFFSET
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1,2
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COMMENT
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Essentially the same as the quarter-squares A002620.
Nonsquare elements of this sequence are given by A002378. - Max Alekseyev (maxale(AT)gmail.com), Nov 27 2006
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FORMULA
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a(n) = (n + n mod 2)*(n + 2 - n mod 2)/4.
Numbers of the form k^2 or k^2 - k. - Don Reble, Oct 17, 2003
a(1) = 1, a(2) = 2, a(n) = n + a(n - 2) - Alonso Delarte (alonso.delarte(AT)gmail.com), Jun 18 2005
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MATHEMATICA
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a[1] := 1; a[2] := 2; a[n_] := n + a[n - 2]; Table[a[n], {n, 57}] (Delarte)
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CROSSREFS
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Cf. A006446, A003059, A002620.
Cf. A002378, A006446.
Sequence in context: A083392 A076921 A002620 this_sequence A025699 A024617 A025698
Adjacent sequences: A087808 A087809 A087810 this_sequence A087812 A087813 A087814
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KEYWORD
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nonn
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AUTHOR
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Reinhard Zumkeller (reinhard.zumkeller(AT)gmail.com), Oct 16 2003
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