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 A247142 #10 Nov 20 2014 16:59:30 %S A247142 2,3,5,7,11,13,17,19,23,29,31,35,37,41,43,47,49,53,55,59,61,67,71,73, %T A247142 79,83,89,97,101,103,107,109,113,127,131,137,139,145,149,151,157,163, %U A247142 167,173,179,181,191,193,197,199,211,215,223,227,229,233,239,241,251,257,263,269,271,277,281,283,293,307,311,313,317,331,337,341 %N A247142 Numbers for which the root mean square of proper divisors is an integer. %C A247142 All the prime numbers (A000040) are in this sequence. But there are other numbers (A247135). %H A247142 Daniel Lignon, <a href="/A247142/b247142.txt">Table of n, a(n) for n = 1..1249</a> %t A247142 Select[Range[2,1000],IntegerQ[RootMeanSquare[Most[Divisors[#]]]]&] %Y A247142 Cf. A140480 (RMS of all divisors is an integer). %K A247142 nonn %O A247142 1,1 %A A247142 _Daniel Lignon_, Nov 20 2014