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 A063664 Numbers whose reciprocal is the sum of two reciprocals of squares. 5
 2, 8, 18, 20, 32, 50, 72, 80, 90, 98, 128, 144, 162, 180, 200, 242, 272, 288, 320, 338, 360, 392, 450, 468, 500, 512, 576, 578, 648, 650, 720, 722, 800, 810, 882, 968, 980, 1058, 1088, 1152, 1250, 1280, 1296, 1332, 1352, 1440, 1458, 1568, 1620, 1682, 1800 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS These are numbers which can be written either as b^2*c^2*(b^2+c^2)*d^2 or if (b^2+c^2) is a square then as b^2*c^2*d^2, since 1/(b*(b^2+c^2)*d)^2+1/(c*(b^2+c^2)*d)^2 =1/(b^2*c^2*(b^2+c^2)*d^2) and 1/(b*sqrt(b^2+c^2)*d)^2+1/(c*sqrt(b^2+c^2)*d)^2 = 1/(b^2*c^2*d^2). LINKS EXAMPLE 98 is in the sequence since 1/98=1/10^2+1/70^2 (also 1/98=1/14^2+1/14^2). CROSSREFS Either products of terms in A063663 and A000290, or squares of A008594. Cf. A001481, A000404, A063665, A063669. Sequence in context: A051248 A228615 A267823 * A094147 A117612 A320662 Adjacent sequences:  A063661 A063662 A063663 * A063665 A063666 A063667 KEYWORD nonn AUTHOR Henry Bottomley, Jul 28 2001 EXTENSIONS Offset changed to 1 by Derek Orr, Jun 23 2015 STATUS approved

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Last modified August 14 09:14 EDT 2020. Contains 336480 sequences. (Running on oeis4.)