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 A069834 a(n) = n-th reduced triangular number: n*(n+1)/{2^k} where 2^k is the largest power of 2 that divides product n*(n+1). 9
 1, 3, 3, 5, 15, 21, 7, 9, 45, 55, 33, 39, 91, 105, 15, 17, 153, 171, 95, 105, 231, 253, 69, 75, 325, 351, 189, 203, 435, 465, 31, 33, 561, 595, 315, 333, 703, 741, 195, 205, 861, 903, 473, 495, 1035, 1081, 141, 147, 1225, 1275, 663, 689, 1431, 1485, 385, 399 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS The largest odd divisor of n-th triangular number. GCD(a(n),a(n+1)) = A000265(n+1). - Ralf Stephan, Apr 05 2003 LINKS T. D. Noe, Table of n, a(n) for n = 1..10000 FORMULA a(n) = A000265(n) * A000265(n+1). - Franklin T. Adams-Watters, Nov 20 2009 MATHEMATICA Table[tri = n*(n + 1)/2; tri/2^IntegerExponent[tri, 2], {n, 100}] (* T. D. Noe, Oct 28 2013 *) PROG (PARI) for(n=1, 100, t=n*n+n:while(t%2==0, t=t/2):print1(t", ")) (PARI) a(n)=local(t); t=n*(n+1)\2; t/2^valuation(t, 2) \\ Franklin T. Adams-Watters, Nov 20 2009 CROSSREFS Cf. A000217, A050605. Sequence in context: A183483 A218663 A095355 * A064038 A051684 A209388 Adjacent sequences:  A069831 A069832 A069833 * A069835 A069836 A069837 KEYWORD nonn AUTHOR Amarnath Murthy, Apr 14 2002 EXTENSIONS More terms from Ralf Stephan, Apr 05 2003 STATUS approved

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Last modified June 17 22:17 EDT 2019. Contains 324200 sequences. (Running on oeis4.)