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Search: id:A113502
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| A113502 |
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A number n is included if at least one of its divisors > 1 is a triangle number (i.e. is of the form m(m+1)/2, m >= 2). |
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+0
8
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| 3, 6, 9, 10, 12, 15, 18, 20, 21, 24, 27, 28, 30, 33, 36, 39, 40, 42, 45, 48, 50, 51, 54, 55, 56, 57, 60, 63, 66, 69, 70, 72, 75, 78, 80, 81, 84, 87, 90, 91, 93, 96, 99, 100, 102, 105, 108, 110, 111, 112, 114, 117, 120, 123, 126, 129, 130, 132, 135, 136, 138, 140, 141
(list; graph; listen)
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OFFSET
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1,1
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COMMENT
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n is in the sequence if it is not a "triangle-free" positive integer.
a(n) = A088723(n)/2. - Ray Chandler (rayjchandler(AT)sbcglobal.net), May 29 2008
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EXAMPLE
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12 is included because its divisors are 1, 2, 3, 4, 6, and 12, two of which (3 and
6) are triangular numbers > 1.
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MATHEMATICA
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v={}; Do[If[b=Select[Divisors[n], #>1 && IntegerQ[(1+8#)^(1/2)]&]; b!={}, AppendTo[v, n]], {n, 200}]; v (Firoozbakht)
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CROSSREFS
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Cf. A112886, A000217, A013929.
Sequence in context: A055632 A133006 A055264 this_sequence A061904 A111359 A085782
Adjacent sequences: A113499 A113500 A113501 this_sequence A113503 A113504 A113505
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KEYWORD
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nonn
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AUTHOR
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Leroy Quet (qq-quet(AT)mindspring.com), Jan 10 2006
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EXTENSIONS
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More terms from Farideh Firoozbakht (mymontain(AT)yahoo.com), Jan 12 2006
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