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A092530 a(0) = 0; for n > 0, a(n) = T(n) + k where T(n) is the n-th triangular number (A000217) and k (see A026741) is the smallest positive number such that a(n) is divisible by n. 2

%I #23 Feb 04 2019 02:59:33

%S 0,2,4,9,12,20,24,35,40,54,60,77,84,104,112,135,144,170,180,209,220,

%T 252,264,299,312,350,364,405,420,464,480,527,544,594,612,665,684,740,

%U 760,819,840,902,924,989,1012,1080,1104,1175,1200,1274,1300,1377,1404,1484

%N a(0) = 0; for n > 0, a(n) = T(n) + k where T(n) is the n-th triangular number (A000217) and k (see A026741) is the smallest positive number such that a(n) is divisible by n.

%H Colin Barker, <a href="/A092530/b092530.txt">Table of n, a(n) for n = 0..1000</a>

%H A. W. Vyawahare and K. M. Purohit, <a href="https://core.ac.uk/download/pdf/30438744.pdf">Near pseudo Smarandache function</a>, Smarandache Notions, 14 (2004), 42-61.

%H <a href="/index/Rec#order_05">Index entries for linear recurrences with constant coefficients</a>, signature (1,2,-2,-1,1).

%F a(0) = 0, a(2n) = a(2n-1) + n, a(2n-1) = a(2n-2) + 3n-1. - _Amarnath Murthy_, Jul 04 2004

%F From _Colin Barker_, Feb 03 2019: (Start)

%F G.f.: x*(2 + 2*x + x^2 - x^3) / ((1 - x)^3*(1 + x)^2).

%F a(n) = (n*(2 + n)) / 2 for n even.

%F a(n) = (n*(3 + n)) / 2 for n odd.

%F a(n) = a(n-1) + 2*a(n-2) - 2*a(n-3) - a(n-4) + a(n-5) for n>4.

%F (End)

%p seq(n*(1+ceil(n/2)), n=0..53); # _Zerinvary Lajos_ and _Klaus Brockhaus_, Apr 10 2007

%t {0}~Join~Array[Block[{k = 1}, While[GCD[#1, #2 + k] < #1, k++]; #2 + k] & @@ {#, (#^2 + #)/2} &, 53] (* or *)

%t CoefficientList[Series[x (2 + 2 x + x^2 - x^3)/((1 - x)^3*(1 + x)^2), {x, 0, 53}], x] (* _Michael De Vlieger_, Feb 03 2019 *)

%o (PARI) for(n=0,53,print1(n*(1+ceil(n/2)),",")); // _Klaus Brockhaus_, Apr 10 2007

%o (PARI) concat(0, Vec(x*(2 + 2*x + x^2 - x^3) / ((1 - x)^3*(1 + x)^2) + O(x^40))) \\ _Colin Barker_, Feb 03 2019

%Y Equals A000217 + A026741.

%K nonn,easy

%O 0,2

%A _N. J. A. Sloane_, Apr 08 2004

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Last modified March 28 14:02 EDT 2024. Contains 371254 sequences. (Running on oeis4.)