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 A278048 Let v = list of denominators of Farey series of order n (see A006843); let b(n) = Sum 1/(k*k'*(k+k')), where (k,k') are pairs of successive terms of v; a(n) = denominator of b(n). 2
 2, 3, 30, 21, 252, 396, 6435, 858, 2042040, 3527160, 5290740, 9360540, 1029659400, 617795640, 116454478140, 1061790830100, 283144221360, 10644519600, 14060345939640, 14060345939640, 2960272834318800, 130015019445168, 4653946718775900, 43747099156493460 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 LINKS J. Lehner and M. Newman, Sums involving Farey fractions, Acta Arithmetica 15.2 (1969): 181-187. EXAMPLE The fractions b(n) are 1/2, 1/3, 7/30, 4/21, 37/252, 53/396, 707/6435, 85/858, 179077/2042040, 289613/3527160, 379721/5290740, 641671/9360540, 62836087/1029659400, 35819033/617795640, ... MAPLE Farey := proc(n) sort(convert(`union`({0}, {seq(seq(m/k, m=1..k), k=1..n)}), list)) end: ans:=[]; for n from 1 to 50 do t1:=denom(Farey(n)); t2:=add( 1/(t1[i]*t1[i+1]*(t1[i]+t1[i+1])), i=1..nops(t1)-1); ans:=[op(ans), t2]; od: ans; map(numer, ans); # A278047 map(denom, ans); # A278048 CROSSREFS Cf. A006843, A005728, A240877, A278046, A278047. Sequence in context: A277811 A127615 A210417 * A273467 A278861 A303158 Adjacent sequences:  A278045 A278046 A278047 * A278049 A278050 A278051 KEYWORD nonn,frac AUTHOR N. J. A. Sloane, Nov 22 2016 STATUS approved

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Last modified June 21 19:59 EDT 2021. Contains 345365 sequences. (Running on oeis4.)