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 A083228 #12 Sep 08 2022 08:45:10 %S A083228 1,3,21,341,10923,699051,89478485,22906492245,11728124029611, %T A083228 12009599006321323,24595658764946068821,100743818301219097892181, %U A083228 825293359523586849932749483,13521606402434446949298167524011 %N A083228 A Jacobsthal related sequence. %H A083228 Vincenzo Librandi, <a href="/A083228/b083228.txt">Table of n, a(n) for n = 0..55</a> %F A083228 a(n) = A001045(binomial(n+2, 2)) = 2^binomial(n+2, 2)/3 - (-1)^binomial(n+2, 2)/3. %o A083228 (Magma) [2^Binomial(n+2, 2)/3-(-1)^Binomial(n+2, 2)/3: n in [0..15]]; // _Vincenzo Librandi_, Jun 29 2011 %o A083228 (PARI) a(n)=2^binomial(n+2, 2)\/3 \\ _Charles R Greathouse IV_, Jun 29 2011 %Y A083228 Cf. A000217. %K A083228 easy,nonn %O A083228 0,2 %A A083228 _Paul Barry_, Apr 23 2003