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 A118017 Largest denominators in even Egyptian fraction representation of 1. 0
 12, 84, 3612, 6526884, 21300113901612 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS An Egyptian Fraction representation of a rational number a/b is a list of distinct unit fractions with sum a/b.  We will call it an even Egyptian Fraction representation if only even integers are used as denominators.  The n-th term of this sequence gives the largest denominators that appear in an Egyptian Fraction Representation of one with length n+3. For instance, 1/2 + 1/4 + 1/6 +1/12 gives a 4 term even representation of one, which is the shortest possible Egyptian even fraction representation of one. This sequence can be derived from the Sylvester sequence (A000058). If s(n) represents the Sylvester sequence, s(n)-1 is the largest denominator appearing in an n term Egyptian fraction representation of 1. There is a one to one correspondence between k term representations and k+1 term even representation for k<12. An even representation has to have at least 4 terms, thus a(1) is related to s(3). a(1)=2*(s(3)-1), etc. Excluding the first two terms of the Pythagorean spiral sequence (A053631) yields this sequence. LINKS FORMULA a(n+1)=1/2*a(n)^2+a(n) EXAMPLE a(2)=1/2*12^2+12 so a(2)=84 CROSSREFS Cf. A000058, A053631, A007018. A053631 and A127690 are very similar to this sequence. Sequence in context: A003209 A155645 A095267 * A225785 A098206 A104911 Adjacent sequences:  A118014 A118015 A118016 * A118018 A118019 A118020 KEYWORD nonn AUTHOR Teena Carroll, Jul 06 2011 STATUS approved

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