OFFSET
1,1
COMMENTS
Squarefree terms of A003273.
Assuming the Birch and Swinnerton-Dyer conjecture, determining whether a number n is congruent requires counting the solutions to a pair of equations. For odd n, see A072068 and A072069; for even n see A072070 and A072071. The Mathematica program for this sequence uses variables defined in A072068, A072069, A072070, A072071. - T. D. Noe, Jun 13 2002
REFERENCES
Albert H. Beiler, Recreations in the theory of numbers, New York, Dover, (2nd ed.) 1966. See p. 155.
R. K. Guy, Unsolved Problems in Number Theory, D27.
N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).
LINKS
R. Alter and T. B. Curtz, A note on congruent numbers, Math. Comp., 28 (1974), 303-305 and 30 (1976), 198.
American Institute of Mathematics, A trillion triangles
Jose Aranda, C++ program
B. Cipra, Tallying the class of congruent numbers, ScienceNOW, Sep 23 2009.
Clay Mathematics Institute, The Birch and Swinnerton-Dyer Conjecture
Keith Conrad, The Congruent Number Problem, The Harvard College Mathematics Review, 2008.
Department of Pure Maths., Univ. Sheffield, Pythagorean triples and the congruent number problem
A. Dujella, A. S. Janfeda, and S. Salami, A Search for High Rank Congruent Number Elliptic Curves, JIS 12 (2009) 09.5.8.
Hisanori Mishima, 361 Congruent Numbers g: 1<=g<=999
Giovanni Resta, Congruent numbers Primitive congruent numbers up to 10^7.
Karl Rubin, Elliptic curves and right triangles
J. B. Tunnell, A classical Diophantine problem and modular forms of weight 3/2, Invent. Math., 72 (1983), 323-334.
Wikipedia, Congruent number
R. G. Wilson v, Letter to N. J. A. Sloane, Oct. 1993
EXAMPLE
6 is congruent because 6 is the area of the right triangle with sides 3,4,5. It is a primitive congruent number because it is squarefree.
MATHEMATICA
(* The following Mathematica code assumes the truth of the Birch and Swinnerton-Dyer conjecture and uses functions from A072068. *)
For[lst={}; n=1, n<=maxN, n++, If[SquareFreeQ[n], If[(EvenQ[n]&&soln3[[n/2]]==2soln4[[n/2]])|| (OddQ[n]&&soln1[[(n+1)/2]]==2soln2[[(n+1)/2]]), AppendTo[lst, n]]]]; lst
(* The following self-contained Mathematica code also assumes the truth of the Birch and Swinnerton-Dyer conjecture. *)
CongruentQ[n_] := Module[{x, y, z, ok=False}, (Which[! SquareFreeQ[n], Null[], MemberQ[{5, 6, 7}, Mod[n, 8]], ok = True, OddQ@n&&Length@Solve[x^2+2y^2+8z^2==n, {x, y, z}, Integers]==2Length@Solve[x^2+2y^2+32z^2==n, {x, y, z}, Integers], ok=True, EvenQ@n&&Length@Solve[x^2+4y^2+8z^2==n/2, {x, y, z}, Integers]==2Length@ Solve[x^2 + 4 y^2 + 32 z^2 == n/2, {x, y, z}, Integers], ok=True]; ok)]; Select[Range[200], CongruentQ] (* Frank M Jackson, Jun 06 2016 *)
CROSSREFS
KEYWORD
nonn
AUTHOR
EXTENSIONS
More terms from T. D. Noe, Feb 26 2003
STATUS
approved