OFFSET
1,2
COMMENTS
Those numbers seem to be congruent to 0,1,-1 mod 5. - Ctibor O. Zizka, Sep 23 2008
No, the first terms congruent to 2 and 3 mod 5 are a(461) = 247511537 and a(1603) = 7177834573, respectively. - Giovanni Resta, Oct 29 2019
LINKS
Giovanni Resta, Table of n, a(n) for n = 1..7430 (terms 1..455 from Andrew Weimholt, terms 456..1660 from Donovan Johnson)
EXAMPLE
a(5)=145, because A140480(5)=287, with divisors 1,7,41,287 and RMS(1,7,41,287) = 145.
MATHEMATICA
rmsQ[n_] := IntegerQ[Sqrt[DivisorSigma[2, n]/DivisorSigma[0, n]]]; Reap[ For[k=1; n=1, k<10^7, k++, If[rmsQ[k], an = Sqrt[Mean[Divisors[k]^2]]; Print["k = ", k, " a(", n++, ") = ", an]; Sow[an]]]][[2, 1]] (* Jean-François Alcover, Dec 04 2015 *)
PROG
(PARI) for(n=1, 1e6, if(issquare(sumdiv(n, d, d^2)/numdiv(n), &s) && denominator(s)==1, print1(s", "))) \\ Charles R Greathouse IV, Mar 08 2013
CROSSREFS
KEYWORD
nonn
AUTHOR
Andrew Weimholt, Jul 07 2008
STATUS
approved