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 A074935 Denominator of a(n), where for n > 2, a(n)=-1/a(n-1)+1/a(n-2), a(1)=1, a(2)=2. 1
 1, 1, 2, 2, 3, 24, 200, 6675, 3045936, 46360115600, 251445391554623475, 23318100352452485482468409184 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,3 COMMENTS a(n)->-(-1)^n sqrt(2), a slowly converging sequence. In general, for recursive sequence: a(n)=Sum[i=1,...,k +/- Sqrt[Sum[i=1,..,k,abs[c(i)]]], independently on initial a(i). LINKS FORMULA a(n>2)=-1/a(n-1)+1/a(n-2), a(1)=1, a(2)=2, a(n)->-(-1)^n sqrt(2). EXAMPLE a(3)=-1/a(2)+1/a(1)=-1/2+1=1/2, therefore in the sequence, 3rd term is 2. MATHEMATICA RecurrenceTable[{a[1]==1, a[2]==2, a[n]==-1/a[n-1]+1/a[n-2]}, a, {n, 13}]// Denominator (* Harvey P. Dale, Jul 21 2019 *) CROSSREFS Cf. A076655. Sequence in context: A189254 A036503 A109590 * A320103 A212796 A078239 Adjacent sequences:  A074932 A074933 A074934 * A074936 A074937 A074938 KEYWORD nonn,frac AUTHOR Zak Seidov, Oct 24 2002 STATUS approved

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Last modified April 11 18:00 EDT 2021. Contains 342888 sequences. (Running on oeis4.)