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 A236391 Positive numbers n such that 100*n^2/(100+n^2) are integers. 0
 5, 10, 20, 30, 70 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS Rewrite 100n^2/(100+n^2) as an I : n=sqrt(100I/(100-I)), where a finite substitution for I results. Instead of 100, we could use 72 and get n=8,24,48,64; we could use 162 and get n=54,108,144,150. Many other values are possible. LINKS EXAMPLE for n=20, 100*20^2/(100+20^2)=I or 80. MATHEMATICA Select[Range[1000], IntegerQ[100*#^2/(100 + #^2)] &] (* T. D. Noe, Jan 29 2014 *) CROSSREFS Cf. A162688. Sequence in context: A306775 A027884 A331141 * A026357 A117518 A107486 Adjacent sequences:  A236388 A236389 A236390 * A236392 A236393 A236394 KEYWORD nonn,fini,full AUTHOR Larry J Zimmermann, Jan 24 2014 STATUS approved

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Last modified August 10 16:24 EDT 2022. Contains 356039 sequences. (Running on oeis4.)