cp's OEIS Frontend

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.

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A272389 Longest side of primitive Heronian tetrahedron.

Original entry on oeis.org

117, 160, 203, 225, 318, 319, 319
Offset: 1

Views

Author

Albert Lau, May 21 2016

Keywords

Comments

A Heronian tetrahedron or perfect tetrahedron is a tetrahedron whose edge lengths, face areas and volume are all integers.
Primitive tetrahedron means 6 sides don't share a common factor.

Examples

			see A272388
		

Crossrefs

Programs

  • Mathematica
    aMax=360(*WARNING:takes a long time*);
    heron=1/4Sqrt[(#1+#2+#3)(-#1+#2+#3)(#1-#2+#3)(#1+#2-#3)]&;
    cayley=1/24Sqrt[2Det[{
      {0,1,1,1,1},
      {1,0,#1^2,#2^2,#6^2},
      {1,#1^2,0,#3^2,#5^2},
      {1,#2^2,#3^2,0,#4^2},
      {1,#6^2,#5^2,#4^2,0}
    }]]&;
    Do[
      S1=heron[a,b,c];
      If[S1//IntegerQ//Not,Continue[]];
      Do[
        S2=heron[a,e,f];
        If[S2//IntegerQ//Not,Continue[]];
        Do[
          If[GCD[a, b, c, d, e, f] > 1, Continue[]];
          If[b==e&&c>f||b==f&&c>e,Continue[]];
          S3=heron[b,d,f];
          If[S3//IntegerQ//Not,Continue[]];
          S4=heron[c,d,e];
          If[S4//IntegerQ//Not,Continue[]];
          V=cayley[a,b,c,d,e,f];
          If[V//IntegerQ//Not,Continue[]];
          If[V==0,Continue[]];
          a//Sow(*{a,b,c,d,e,f,S1,S2,S3,S4,V}//Sow*);
        ,{d,Sqrt[((b^2-c^2+e^2-f^2)/(2a))^2+4((S1-S2)/a)^2]//Ceiling,Min[a,Sqrt[((b^2-c^2+e^2-f^2)/(2a))^2+4((S1+S2)/a)^2]]}];
      ,{e,a-b+1,b},{f,a-e+1,b}];
    ,{a,117,aMax},{b,a/2//Ceiling,a},{c,a-b+1,b}]//Reap//Last//Last
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