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A140089 Products of two triangular numbers each > 1.

%I A140089 #11 Jul 31 2024 09:35:59
%S A140089 9,18,30,36,45,60,63,84,90,100,108,126,135,150,165,168,198,210,216,
%T A140089 225,234,270,273,280,315,330,360,396,408,420,441,450,459,468,513,540,
%U A140089 546,550,570,588,630,660,675,693,720,756,759,780,784,816,825,828,900,910
%N A140089 Products of two triangular numbers each > 1.
%p A140089 isA140089 := proc(n)
%p A140089     for d in numtheory[divisors](n) minus {1} do
%p A140089         if d^2 > n then
%p A140089             return false;
%p A140089         end if;
%p A140089         if isA000217(d) then
%p A140089             if isA000217(n/d) then
%p A140089                 return true;
%p A140089             end if;
%p A140089         end if;
%p A140089     end do:
%p A140089     return false;
%p A140089 end proc:
%p A140089 for n from 1 to 1000 do
%p A140089     if isA140089(n) then
%p A140089         printf("%d,",n) ;
%p A140089     end if;
%p A140089 end do: # _R. J. Mathar_, Jul 31 2024
%Y A140089 Cf. A000217. Subsequence of A085780.
%K A140089 nonn
%O A140089 1,1
%A A140089 _N. J. A. Sloane_, Jun 27 2008
%E A140089 More terms from _Rick L. Shepherd_ and _John W. Layman_, Jul 03 2008