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Research notes on every problem, and a library of the papers behind them. Built from the open erdos repository.

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Claim. For a fixed index kk (the paper states no range; its derivation and its check at k=1k=1 treat kk as a positive integer),

∑n≥01F2nk={2Lk−F2k5+5Fk22F2kk odd,2−Fk5+Lk2Fkk even,\sum_{n\ge0}\frac{1}{F_{2^nk}}= \begin{cases} \dfrac{2L_k-F_{2k}\sqrt5+5F_k^2}{2F_{2k}} & k \text{ odd},\\[2ex] \dfrac{2-F_k\sqrt5+L_k}{2F_k} & k \text{ even}, \end{cases}

where LkL_k is the kk-th Lucas number. In both cases the coefficient of 5\sqrt5 is −1/2-1/2 and the other terms are rational, so each sum is irrational and the instances nj=2jkn_j=2^jk of Problem 267 have answer yes; that inference is this page's, since the paper evaluates the sums and does not discuss their irrationality. The case k=1k=1 recovers Good's value (7−5)/2(7-\sqrt5)/2. The paper gives no theorem numbers; the closed form is stated on its page 455 (result page). The method telescopes the identity F2k=FkLkF_{2k}=F_kL_k with the Lucas identities Lm+p+Lm−p=LmLpL_{m+p}+L_{m-p}=L_mL_p (pp even) and Lk2=L2k+2(−1)kL_k^2=L_{2k}+2(-1)^k, sums the resulting Lucas series with a summation formula of Siler, and passes to the limit through powers of (1±5)/2(1\pm\sqrt5)/2. The source is V. E. Hoggatt, Jr. and Marjorie Bicknell, A reciprocal series of Fibonacci numbers with subscripts 2nk2^nk, Fibonacci Quart. 14 (1976), no. 5, 453–455, on the card hoggattjr_1976_reciprocal_series_fibonacci_numbers_subscripts.

Covers. The instances nj=2jkn_j=2^jk for every positive integer kk, the case k=1k=1 being Good's instance nj=2jn_j=2^j (the Good page): the answer is yes. Not covered: every other index sequence. All these instances lie inside Badea's 1993 condition (the Badea page).

Acceptance. Refereed: The Fibonacci Quarterly, volume 14, number 5 (December 1976). The site's commentary credits Bicknell and Hoggatt, with Good, with the irrationality of the sum over the indices 2n2^n but labels the problem OPEN, so that commentary is not listed as reviewed evidence. The corpus has not reproved the closed form and awards no tier of its own.

Depends on. Nothing in this wiki; the claim rests on the cited paper.