This site is supported by donations to The OEIS Foundation.

 Please make a donation to keep the OEIS running. We are now in our 55th year. In the past year we added 12000 new sequences and reached 8000 citations (which often say "discovered thanks to the OEIS"). We need to raise money to hire someone to manage submissions, which would reduce the load on our editors and speed up editing. Other ways to donate

 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 A007237 Number of triangles with integer sides and area = n times perimeter. (Formerly M3878) 7
 5, 18, 45, 45, 52, 139, 80, 89, 184, 145, 103, 312, 96, 225, 379, 169, 116, 498, 123, 328, 560, 280, 134, 592, 228, 271, 452, 510, 134, 1036, 144, 280, 639, 339, 597, 1119, 139, 354, 635, 648, 162, 1486, 169, 594, 1215, 354, 186, 1066, 369, 622 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 REFERENCES N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence). LINKS Ray Chandler, Table of n, a(n) for n = 1..5000 (first 300 terms from Zhining Yang) Juan V. Savall and Jesus Ferrer, Problem E3408, Amer. Math. Monthly, 99 (1992), 175-176. FORMULA a(n) = A120062(2n). - Ray Chandler, Jul 27 2017 EXAMPLE For n=2, the a(2)=18 solutions whose area is twice its perimeter: (13,14,15) (12,16,20) (15,15,24) (10,24,26) (11,25,30) (18,20,34) (15,26,37) (14,30,40) (10,35,39) (9,40,41) (12,50,58) (33,34,65) (25,51,74) (9,75,78) (11,90,97) (21,85,104) (19,153,170) (18,289,305). PROG (PARI) for(k=1, 100, n=0; d=4*k^2; e=3*d; for(b=1, sqrt(e), for(c=2*k, e/b, if(b*c>d && c>=b, f = (b + c)*d / (b * c - d); if(f>=c, a=floor(f); if(a==f, n++))))); print1(n, ", ")) CROSSREFS Sequence in context: A101105 A037140 A321049 * A327842 A000339 A270944 Adjacent sequences:  A007234 A007235 A007236 * A007238 A007239 A007240 KEYWORD nonn AUTHOR EXTENSIONS a(16)-a(50) from Les Reid, Jul 06 2010 STATUS approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recent
The OEIS Community | Maintained by The OEIS Foundation Inc.

Last modified December 12 15:11 EST 2019. Contains 329960 sequences. (Running on oeis4.)