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A076982 Number of triangular numbers that divide the n-th triangular number. 6
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; text; internal format)
OFFSET

1,2

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

LINKS

T. D. Noe, Table of n, a(n) for n = 1..10000

FORMULA

a(n) = A007862(A000217(n)) = A129308(A002378(n)). - Ray Chandler, Jun 21 2008

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);

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 *)

CROSSREFS

Cf. A076983, A084260.

Sequence in context: A276857 A244893 A321478 * A283617 A164886 A091935

Adjacent sequences:  A076979 A076980 A076981 * A076983 A076984 A076985

KEYWORD

nonn

AUTHOR

Amarnath Murthy, Oct 25 2002

EXTENSIONS

More terms from Lior Manor Nov 06 2002

More terms from Sascha Kurz, Jan 26 2003

STATUS

approved

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Last modified June 19 19:09 EDT 2019. Contains 324222 sequences. (Running on oeis4.)