This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A072389 #23 Jul 02 2025 16:02:01
%S A072389 0,4,12,24,36,40,60,72,84,112,120,144,180,220,240,252,264,312,336,360,
%T A072389 364,400,420,432,480,504,540,544,600,612,660,672,684,760,792,840,864,
%U A072389 900,924,936,1012,1080,1092,1104,1120,1200,1260,1300,1320
%N A072389 Numbers of the form x*(x+1) * y*(y+1) ("bipronics") with x and y nonnegative integers.
%C A072389 Nonnegative numbers k = a*b = c*d, where a+b = c+d+1. - _Yifan Xie_, Jun 28 2024
%H A072389 John Drake, <a href="/A072389/b072389.txt">Table of n, a(n) for n = 1..10000</a>
%e A072389 a(3) = 1*2*2*3 = 12.
%o A072389 (PARI) A003056(n)=(sqrtint(8*n+1)-1)\2
%o A072389 list(lim)=my(v=List([0]), t); for(a=1, A003056(lim\4), t=a*(a+1); for(b=a, A003056(lim\t\2), listput(v, b*(b+1)*t))); Set(v) \\ _Charles R Greathouse IV_, Jul 11 2024
%Y A072389 Cf. A053990 (sequence of bipronics with x and y distinct).
%Y A072389 Cf. A085780 (one quarter of this).
%K A072389 nonn,easy
%O A072389 1,2
%A A072389 Stuart M. Ellerstein (ellerstein(AT)aol.com), Jul 20 2002
%E A072389 More terms from _James Sellers_, Jul 23 2002