%I #13 May 16 2020 02:25:16

%S 6,18,36,48,60,90,126,144,162,168,210,216,252,270,288,330,360,378,384,

%T 396,468,480,486,540,546,594,630,720,750,792,816,858,918,924,972,990,

%U 1008,1026,1140,1152,1170,1260,1296,1344,1386,1404,1518,1530,1560,1620,1638,1656,1680,1728,1800

%N Numbers k that can be represented in the form k = p^3 - q^3 - r^3, where p, q, r are positive integers satisfying p = q + r.

%C An alternative representation of k is k = 3*q*r*(q+r), with q, r positive integers, then k is a multiple of 6.

%F a(n) = 6 * A121741(n).

%e 60 is in the sequence because 60 = 5^3 - 4^3 - 1^3, with 5 = 4 + 1.

%o (PARI) ok(n) = {my(i=1, a=0, m=0, j); if(n%6==0, while(a<=n&&m==0, j=1; while(j<i&&m==0, a=3*i*j*(i-j); if(a==n, m=1); j+=1); i+=1)); m}

%Y Cf. A000578, A003072, A024975, A078129, A255018, A275154.

%K nonn

%O 1,1

%A _Antonio Roldán_, Apr 06 2020