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 A287733 First differences of A069497. 1
 6, 30, 30, 12, 42, 90, 66, 24, 78, 150, 102, 36, 114, 210, 138, 48, 150, 270, 174, 60, 186, 330, 210, 72, 222, 390, 246, 84, 258, 450, 282, 96, 294, 510, 318, 108, 330, 570, 354, 120, 366, 630, 390, 132, 402, 690, 426, 144, 438, 750, 462, 156, 474, 810, 498, 168, 510, 870, 534 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS First differences of the subsequence of triangular numbers that are divisible by 6. By definition, these numbers are themselves divisible by 6. LINKS FORMULA G.f.: 6*(x^2+4*x+1)*(x^2-x+1)/((x-1)^2*(x^2+1)^2). - Robert Israel, May 30 2017 EXAMPLE The first triangular number divisible by 6 is 6, and the second triangular number divisible by 6 is 36.  Therefore a(2) = 36 - 6 = 30. (The zeroeth triangular number divisible by 6 is taken to be 0.) MAPLE S:= [seq(seq((12*i+j)*(12*i+j+1)/2, j=[0, 3, 8, 11]), i=0..50)]: S[2..-1]-S[1..-2]; # Robert Israel, May 30 2017 MATHEMATICA Differences@ Select[Array[# (# + 1)/2 &, 180, 0], Mod[#, 6] == 0 &] (* Robert G. Wilson v, May 30 2017 *) Differences[Select[Accumulate[Range[0, 209]], Divisible[#, 6] &]] (* Alonso del Arte, May 31 2017 *) CROSSREFS Cf. A069497, A108782, A154293. Sequence in context: A309253 A260017 A123624 * A066197 A078638 A068510 Adjacent sequences:  A287730 A287731 A287732 * A287734 A287735 A287736 KEYWORD nonn,look AUTHOR Greg Huber, May 30 2017 EXTENSIONS More terms from Robert G. Wilson v, May 30 2017 STATUS approved

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Last modified June 13 03:46 EDT 2021. Contains 344980 sequences. (Running on oeis4.)