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 A043328 #7 Jul 09 2025 03:50:39 %S A043328 1,1,2,3,6,11,22,42,83,162,318,623,1224,2402,4717,9261,18185,35706, %T A043328 70111,137665,270313,530772,1042200,2046413,4018242,7890029,15492492, %U A043328 30420327,59731927,117286804,230298862,452204027,887926594,1743490958 %N A043328 a(0)=1; a(1)=1; a(n)= a(n-1) + floor(sqrt(a(n-1)*a(n-2))) + floor(sqrt(a(n-3)*a(n-4))) + .... %C A043328 Nonlinear recurrence similar to that for Narayana numbers. %t A043328 a[ 0 ]=0; a[ 1 ]=1; a[ 2 ]=1; a[ n_Integer ] := a[ n ]=a[ n-1 ]+ Plus@@Map[ Floor[ Sqrt[ Times@@# ] ]&, Partition[ Reverse[ Array[ a, n, 0 ] ], 2 ] ] %Y A043328 Cf. A002083, A043327. %K A043328 nonn,easy %O A043328 0,3 %A A043328 _Olivier Gérard_, Jul 18 2001