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Search: id:A127731
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| A127731 |
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Triangle read by rows, where row n consists of the r's where r = (n*m)/(n+m), and the m's are positive integers such that (n+m) divides (n*m). |
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2
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| 1, 2, 2, 3, 4, 2, 3, 4, 5, 6, 4, 6, 7, 6, 8, 5, 6, 8, 9, 10, 3, 4, 6, 8, 9, 10, 11, 12, 7, 10, 12, 13, 6, 10, 12, 14, 8, 12, 14, 15, 16, 6, 9, 12, 14, 15, 16, 17, 18, 4, 10, 12, 15, 16, 18, 19, 12, 14, 18, 20, 11, 18, 20, 21, 22, 6, 8, 12, 15, 16, 18, 20, 21, 22, 23, 20, 24, 13, 22, 24, 25
(list; graph; listen)
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OFFSET
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2,2
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COMMENT
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The maximum term of the n-th row, for n >= 2, is (n-1). The minimum term of row n is A063428(n), for n >= 3. Row n contains A063647(n) terms (according to a comment by Benoit Cloitre). For p prime, row p^k has k terms. (Each term in row p^k is of the form p^(k-j)*(p^j -1), 1<=j<=k.)
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EXAMPLE
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Row 6 is (2,3,4,5) because row 6 of irregular array A127730 is (3,6,12,30); and (6*3)/(6+3) = 2, (6*6)/(6+6) = 3, (6*12)/(6+12) = 4, and (6*30)/(6+30) = 5.
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MATHEMATICA
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f[n_] := Select[Table[n*m/(n + m), {m, n^2}], IntegerQ]; Table[f[n], {n, 2, 26}] // Flatten(*Chandler*)
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CROSSREFS
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Cf. A063428, A063647, A127730.
Sequence in context: A002122 A105689 A117632 this_sequence A098223 A114892 A077769
Adjacent sequences: A127728 A127729 A127730 this_sequence A127732 A127733 A127734
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KEYWORD
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nonn,tabf
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AUTHOR
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Leroy Quet (qq-quet(AT)mindspring.com), Jan 26 2007
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EXTENSIONS
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Extended by Ray Chandler (rayjchandler(AT)sbcglobal.net), Feb 13 2007
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