This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A165988 #18 Mar 16 2018 07:23:28
%S A165988 0,3,12,9,24,15,36,21,48,27,60,33,72,39,84,45,96,51,108,57,120,63,132,
%T A165988 69,144,75,156,81,168,87,180,93,192,99,204,105,216,111,228,117,240,
%U A165988 123,252,129,264,135,276,141,288,147,300,153,312,159,324,165,336,171,348,177
%N A165988 First trisection of A022998.
%C A165988 Read modulo 10, this yields a sequence with a period of length 10 containing all 10 digits: 0, 3, 2, 9, 4, 5, 6, 1, 8, 7.
%C A165988 The other two trisections start 1, 8, 7, 20, 13, 32, 19, 44.... and 4, 5, 16, 11, 28, 17, 40, 23....
%C A165988 The Pisano period lengths for reading the sequence modulo m>=1 are 1, 2, 1, 4, 10, 2, 14, 8, 6, 10, 22, 4, 26, 14, 10, 16, 34, 6, 38, 20, 14, 22, 46, 8, 50, 26, 18, 28, 58... - _R. J. Mathar_, Oct 08 2011
%H A165988 G. C. Greubel, <a href="/A165988/b165988.txt">Table of n, a(n) for n = 0..5000</a>
%H A165988 <a href="/index/Rec#order_04">Index entries for linear recurrences with constant coefficients</a>, signature (0,2,0,-1).
%F A165988 a(n) = A022998(3n) = 3*A022998(n) = 3*n*(3 +(-1)^n)/2 .
%F A165988 a(n) = 2*a(n-2) - a(n-4).
%F A165988 G.f.: 3*x*(1+4*x+x^2)/((x-1)^2 *(1+x)^2).
%F A165988 E.g.f.: 3*x*(-1 + 3*exp(2*x))*exp(-x)/2. - _Ilya Gutkovskiy_, Apr 21 2016
%t A165988 LinearRecurrence[{0, 2, 0, -1}, {0, 3, 12, 9}, 50] (* _G. C. Greubel_, Apr 20 2016 *)
%o A165988 (PARI) a(n) = my(n=3*n); if (n % 2, n, 2*n); \\ _Michel Marcus_, Apr 21 2016
%Y A165988 Cf. A165351, A165355, A165367.
%K A165988 nonn,easy
%O A165988 0,2
%A A165988 _Paul Curtz_, Oct 03 2009