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.

A051585 Number of integer-sided triangles of area 6n.

Original entry on oeis.org

1, 2, 0, 2, 1, 2, 1, 2, 1, 4, 1, 1, 0, 4, 2, 2, 0, 2, 1, 4, 3, 1, 0, 2, 1, 2, 0, 4, 0, 2, 0, 2, 1, 1, 6, 3, 0, 0, 1, 5, 0, 3, 0, 3, 2, 0, 0, 2, 1, 4, 1, 0, 0, 2, 4, 8, 0, 0, 0, 5, 0, 0, 1, 2, 1, 3, 0, 1, 0, 15, 0, 2, 0, 0, 0, 4, 2, 1, 0, 5, 1, 0, 0, 6, 2, 0, 1, 3, 0, 4, 3, 0, 0, 0, 1, 2, 0, 2, 1, 2, 0, 0, 0
Offset: 1

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If integer-sided triangle has integer area, area is divisible by 6.

Crossrefs

Programs

  • PARI
    a(n)=sum(z=sqrtint(sqrtint(192*n^2)-1)+1,sqrtint(9*(64*n^2+5)\20), sum(y=z\2+1,z, my(t=(y*z)^2-(12*n)^2,x); if(issquare(t,&t), (issquare(y^2+z^2-2*t,&x) && x<=y) + (t && issquare(y^2+z^2+2*t,&x) && x<=y), 0))) \\ Charles R Greathouse IV, Jun 27 2013