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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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7
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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; refs; listen; history; internal format)
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OFFSET
| 1,1
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COMMENTS
| 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
| 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
| 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
| Cf. A112886, A000217, A013929.
Sequence in context: A055632 A133006 A055264 * A061904 A206284 A188299
Adjacent sequences: A113499 A113500 A113501 * A113503 A113504 A113505
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KEYWORD
| nonn
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AUTHOR
| Leroy Quet Jan 10 2006
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EXTENSIONS
| More terms from Farideh Firoozbakht (mymontain(AT)yahoo.com), Jan 12 2006
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