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 A070755 #18 Feb 22 2017 15:50:05 %S A070755 1,10,35,165,286,455,969,1330,1771,4495,6545,7770,9139,12341,14190, %T A070755 16215,23426,32509,35990,39711,47905,52394,57155,79079,98770,105995, %U A070755 121485,129766,138415,176851,198485,221815,246905 %N A070755 Squarefree tetrahedral numbers. %H A070755 Charles R Greathouse IV, <a href="/A070755/b070755.txt">Table of n, a(n) for n = 1..10000</a> %e A070755 286 = 2*11*13 is squarefree and 286 = (13*12*11)/(1*2*3) = Binomial(13,3), so 286 is a term. %p A070755 with(numtheory): A070755:=n->`if`(mobius(n*(n+1)*(n+2)/6)^2=1,n*(n+1)*(n+2)/6,NULL): seq(A070755(n), n=1..100); # _Wesley Ivan Hurt_, Oct 10 2014 %o A070755 (PARI) list(lim)=my(v=List(),t); forstep(n=1,sqrtnint(lim\1*6,3),[2,2,4], if(issquarefree(n/gcd(n,6)) && issquarefree((n+1)/gcd(n+1,6)) && issquarefree((n+2)/gcd(n+2,6)) && (t=binomial(n+2,3))<=lim, listput(v,t))); Vec(v) \\ _Charles R Greathouse IV_, Feb 22 2017 %Y A070755 Intersection of A000292 and A005117. %Y A070755 Cf. A000292 (tetrahedral), A005117 (squarefree), A061304 (squarefree triangular). %K A070755 nonn %O A070755 1,2 %A A070755 _Reinhard Zumkeller_, May 14 2002