OFFSET
1,1
LINKS
Antonio Roldán, Table of n, a(n) for n = 1..8055 (terms <= 10^5)
EXAMPLE
186 is a term because the sum of its triangular divisors, 1+3+6 = 10 is also triangular.
MATHEMATICA
triQ[n_] := n > 1 && IntegerQ[Sqrt[8*n+1]]; q[n_] := triQ[1 + DivisorSum[n, #&, triQ[#] &]]; Select[Range[700], q] (* Amiram Eldar, Aug 12 2023 *)
PROG
(PARI) istriangular(n)=issquare(8*n+1)
{t=0; for(n=1, 10^5, k=sumdiv(n, d, istriangular(d)*d); if(istriangular(k)&&k>>1, t+=1; write("b209309.txt", t, " ", n)))}
CROSSREFS
KEYWORD
nonn
AUTHOR
Antonio Roldán, Jan 18 2013
STATUS
approved