A140089 Products of two triangular numbers each > 1.

9, 18, 30, 36, 45, 60, 63, 84, 90, 100, 108, 126, 135, 150, 165, 168, 198, 210, 216, 225, 234, 270, 273, 280, 315, 330, 360, 396, 408, 420, 441, 450, 459, 468, 513, 540, 546, 550, 570, 588, 630, 660, 675, 693, 720, 756, 759, 780, 784, 816, 825, 828, 900, 910

Offset: 1

Author

N. J. A. Sloane, Jun 27 2008

Keywords

• nonn

Crossrefs

Cf. A000217. Subsequence of A085780.

Programs

Maple

isA140089 := proc(n)
    for d in numtheory[divisors](n) minus {1} do
        if d^2 > n then
            return false;
        end if;
        if isA000217(d) then
            if isA000217(n/d) then
                return true;
            end if;
        end if;
    end do:
    return false;
end proc:
for n from 1 to 1000 do
    if isA140089(n) then
        printf("%d,",n) ;
    end if;
end do: # R. J. Mathar, Jul 31 2024

Extensions

More terms from Rick L. Shepherd and John W. Layman, Jul 03 2008