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A076982
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Number of triangular numbers that divide the n-th triangular number.
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5
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1, 2, 3, 2, 3, 3, 2, 4, 4, 2, 4, 4, 2, 5, 6, 2, 3, 3, 3, 8, 4, 2, 4, 6, 2, 3, 5, 2, 4, 4, 2, 5, 3, 2, 10, 4, 2, 3, 7, 3, 4, 4, 2, 9, 5, 2, 4, 6, 2, 4, 5, 2, 3, 6, 5, 6, 3, 2, 6, 6, 2, 4, 7, 3, 5, 3, 2, 4, 6, 2, 5, 5, 2, 4, 7, 2, 6, 3, 3, 9, 3, 2, 5, 10, 2, 3, 5, 2, 5, 8, 3, 4, 3, 2, 8, 4, 2, 5, 10, 3, 3, 3
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,2
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COMMENTS
| Also number of oblong numbers that divide the n-th oblong number.
Sequence A137281 contains the indices of primitive triangular numbers; those that have no triangular divisors other than 1 and itself. - T. D. Noe, Apr 12 2011
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LINKS
| T. D. Noe, Table of n, a(n) for n = 1..10000
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FORMULA
| a(n) = A007862(A000217(n)) = A129308(A002378(n)). - Ray Chandler (rayjchandler(AT)sbcglobal.net), Jun 21 2008
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MAPLE
| a[1] := 1:for i from 1 to 200 do s := 0:for j from 1 to i do if((i*(i+1)/2 mod j*(j+1)/2)=0) then s := s+1:fi:od:a[i] := s:od:seq(a[l], l=1..200);
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MATHEMATICA
| nn = 100; tri = Table[n*(n+1)/2, {n, nn}]; Table[Count[Mod[tri[[n]], Take[tri, n]], 0], {n, nn}] (* T. D. Noe, Apr 12 2011 *)
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CROSSREFS
| Cf. A076983, A084260.
Sequence in context: A030350 A026240 A124474 * A164886 A091935 A086063
Adjacent sequences: A076979 A076980 A076981 * A076983 A076984 A076985
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KEYWORD
| nonn
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AUTHOR
| Amarnath Murthy (amarnath_murthy(AT)yahoo.com), Oct 25 2002
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EXTENSIONS
| More terms from Lior Manor (lior.manor(AT)gmail.com) Nov 06 2002
More terms from Sascha Kurz (sascha.kurz(AT)uni-bayreuth.de), Jan 26 2003
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