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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A382844 Area of the unique primitive Pythagorean triple (a,b,c) such that (a-b+c)/2 = A000045(n) and its long leg and hypotenuse are consecutive natural numbers.

Original entry on oeis.org

0, 0, 0, 6, 30, 180, 840, 3900, 17220, 75174, 323730, 1386264, 5909904, 25136040, 106739256, 452846310, 1920088086, 8138356716, 34486996824, 146121685380, 619066205340, 2622628707270, 11110214972010, 47065148576496, 199375154768160, 844577145104400, 3577713520710960
Offset: 0

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Keywords

Examples

			For n=4, the short leg is A382843(2,1) = 3 and the long leg is A382843(2,2) = 4  so the area is then a(4) = (3 * 4)/2 = 6.
		

References

  • Miguel Ángel Pérez García-Ortega, José Manuel Sánchez Muñoz and José Miguel Blanco Casado, El Libro de las Ternas Pitagóricas, Preprint 2025.

Crossrefs

Programs

  • Mathematica
    a=Table[Fibonacci[n],{n,0,26}];Apply[Join,Map[{#(#-1)(2#-1)}&,a]]

Formula

a(n) = (A382843(n,1) * A382843(n,2))/2.
a(n) = Fibonacci(n)*(Fibonacci(n) - 1)*(2*Fibonacci(n) - 1).

A382843 Length of the long leg in the unique primitive Pythagorean triple (x,y,z) such that (x-y+z)/2 = A000045(n) and its long leg and hypotenuse are consecutive natural numbers.

Original entry on oeis.org

0, 0, 0, 4, 12, 40, 112, 312, 840, 2244, 5940, 15664, 41184, 108112, 283504, 742980, 1946364, 5097624, 13348944, 34953160, 91516920, 239607940, 627323620, 1642389984, 4299890112, 11257351200, 29472278112, 77159668612, 202007027820, 528861900424, 1384579459120
Offset: 0

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Author

Keywords

Examples

			Triples begin:
  n=0:     -1,     0,     1;
  n=1:      1,     0,     1;
  n=2:      1,     0,     1;
  n=3:      3,     4,     5.
This sequence gives column 2.
		

Crossrefs

Cf. A000045, A382844 (area), A382845 (sum of the legs), A095122 (semiperimeter), A001595 (short leg).

Formula

a(n) = 2*A000045(n)*(A000045(n) - 1),.

A095122 a(n) = Fibonacci(n)*(2*Fibonacci(n)-1).

Original entry on oeis.org

0, 1, 1, 6, 15, 45, 120, 325, 861, 2278, 5995, 15753, 41328, 108345, 283881, 743590, 1947351, 5099221, 13351528, 34957341, 91523685, 239618886, 627341331, 1642418641, 4299936480, 11257426225, 29472399505, 77159865030, 202007345631, 528862414653, 1384580291160
Offset: 0

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Author

Paul Barry, May 29 2004

Keywords

Comments

a(n) mod 2 = Fibonacci(n) mod 2 = A011655(n).
The unique primitive Pythagorean triple (a,b,c) such that (a-b+c)/2 = A000045(n) and its long leg and hypotenuse are consecutive natural numbers is (2*A000045(n)-1, 2*A000045(n)*(A000045(n)-1), 2*A000045(n)*(A000045(n)-1)+1) and its semiperimeter is a(n). - Miguel-Ángel Pérez García-Ortega, Apr 13 2025

References

  • Miguel Ángel Pérez García-Ortega, José Manuel Sánchez Muñoz and José Miguel Blanco Casado, El Libro de las Ternas Pitagóricas, Preprint 2025.

Crossrefs

Programs

  • Mathematica
    #(2#-1)&/@Fibonacci[Range[0,30]] (* or *) LinearRecurrence[{3,1,-5,-1,1},{0,1,1,6,15},30] (* Harvey P. Dale, Jan 14 2012 *)

Formula

G.f.: x*(1-2*x+2*x^2+x^3)/((1+x)*(1-x-x^2)*(1-3*x+x^2)).
a(n) = 2*(Fibonacci(2n-1)+Fibonacci(2n+1))/5-Fibonacci(n)+4*(-1)^n/5.
a(n) = 2*Lucas(2n)/5-Fibonacci(n)+4*(-1)^n/5.
a(n) = 2*A000032(2n)/5-A000045(n)+4*(-1)^n/5.
a(n) = 3*a(n-1)+a(n-2)-5*a(n-3)-a(n-4)+a(n-5), with a(0)=0, a(1)=1, a(2)=1, a(3)=6, a(4)=15. - Harvey P. Dale, Jan 14 2012
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