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 A072157 Denominator of Sum_{k=1..n} phi(k)/k^2. 2
 1, 4, 36, 72, 1800, 1800, 88200, 176400, 529200, 105840, 12806640, 12806640, 2164322160, 2164322160, 10821610800, 21643221600, 6254891042400, 6254891042400, 2258015666306400, 451603133261280, 451603133261280, 451603133261280, 238898057495217120, 238898057495217120 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 LINKS Vincenzo Librandi, Table of n, a(n) for n = 1..300 EXAMPLE 1, 5/4, 53/36, 115/72, 3163/1800, 3263/1800, 170687/88200, ... MAPLE with(numtheory); seq(denom(add(phi(k)/k^2, k = 1..n)), n = 1..25); # G. C. Greubel, Aug 26 2019 MATHEMATICA Denominator[Table[Sum[EulerPhi[k]/k^2, {k, n}], {n, 30}]] (* Harvey P. Dale, Nov 13 2011 *) PROG (PARI) a(n) = denominator( sum(k=1, n, eulerphi(k)/k^2)); \\ G. C. Greubel, Aug 26 2019 (MAGMA) [Denominator( &+[EulerPhi(k)/k^2: k in [1..n]] ): n in [1..25]]; // G. C. Greubel, Aug 26 2019 (Sage) [denominator( sum(euler_phi(k)/k^2 for k in (1..n)) ) for n in (1..25)] # G. C. Greubel, Aug 26 2019 (GAP) List([1..25], n-> DenominatorRat( Sum([1..n], k-> Phi(k)/k^2) ) ); # G. C. Greubel, Aug 26 2019 CROSSREFS Cf. A072156. Sequence in context: A091722 A053939 A167632 * A075215 A193833 A193183 Adjacent sequences:  A072154 A072155 A072156 * A072158 A072159 A072160 KEYWORD nonn,frac AUTHOR N. J. A. Sloane, Jun 28 2002 STATUS approved

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Last modified May 26 07:53 EDT 2020. Contains 334620 sequences. (Running on oeis4.)