A247142 - OEIS

%I #10 Nov 20 2014 16:59:30

%S 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 79,83,89,97,101,103,107,109,113,127,131,137,139,145,149,151,157,163,

%U 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 Numbers for which the root mean square of proper divisors is an integer.

%C All the prime numbers (A000040) are in this sequence. But there are other numbers (A247135).

%H Daniel Lignon, <a href="/A247142/b247142.txt">Table of n, a(n) for n = 1..1249</a>

%t Select[Range[2,1000],IntegerQ[RootMeanSquare[Most[Divisors[#]]]]&]

%Y Cf. A140480 (RMS of all divisors is an integer).

%K nonn

%O 1,1

%A _Daniel Lignon_, Nov 20 2014