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 A141391 #10 Jul 24 2025 09:21:54
%S A141391 1,7,5,11,28,14,182,70,2,66,1518,462,1540,616,296,600,1950,750,10,730,
%T A141391 2336,876,2436,996,3154,1162,5698,210,1554,3234,1638,5382,1872,23088,
%U A141391 4368,5934,201,4359,77991,7021,13090,4270,12950,74,12802,76466,16954
%N A141391 a(n) is the smallest unused number such that the RMS (Root Mean Square) of a(1) through a(n) is an integer.
%C A141391 Actual RMS values are given by A141392
%H A141391 Giovanni Resta, <a href="/A141391/b141391.txt">Table of n, a(n) for n = 1..200</a>
%e A141391 a(4) = 11. Sqrt(mean(1^2, 7^2, 5^2, k^2)) is an integer for k in {5,11,37}. We have already used 5 for a(3), so 11 is the smallest value available for a(4).
%t A141391 s={1};Do[i=1;Until[!MemberQ[s,i]&&IntegerQ[RootMeanSquare[Append[s,i]]],i++];AppendTo[s,i],{n,46}];s (* _James C. McMahon_, Jul 24 2025 *)
%Y A141391 Cf. A141392, A141393, A141394, A140480.
%K A141391 nonn
%O A141391 1,2
%A A141391 _Andrew Weimholt_, Jun 29 2008