OFFSET
1,2
COMMENTS
c is from (1,3,21,49,74,121,249,590,765,...)
LINKS
Charles R Greathouse IV, Table of n, a(n) for n = 1..1000
EXAMPLE
For n=3 we have (1*1+2*2+2*2)= 3*3 so n=3 belongs to the sequence.
MATHEMATICA
Position[Accumulate[DivisorSigma[0, Range[210000]]^2], _?(IntegerQ[ Sqrt[ #]]&)]//Flatten (* Harvey P. Dale, Jul 17 2016 *)
PROG
(PARI) s=0; for(n=1, 1e7, if(issquare(s+=numdiv(n)^2), print1(n", "))) \\ Charles R Greathouse IV, Feb 21 2011
CROSSREFS
KEYWORD
nonn
AUTHOR
Ctibor O. Zizka, Feb 21 2011
STATUS
approved